You could avoid cutting into the wall with something like this Pondmaster mini-skimmer that sits inside the pond:

http://www.pondmasterstore.com/home/pm1/page_63_11/mini_skimmer.html

This skimmer can sit on the bottom of the pond (if it is shallow enough) or it can be mounted closer to the top of the container wall with anchor straps. I have used one of these for 3 years and it works very well for a smaller pond. You can find one of these for less than $100 from several online vendors.

Thanks camperman, what pump do you use and how is it attached? Is there anyway a pump can be put inside the skimmer?
S

This skimmer is too small for the pump to be placed inside. The pump screws onto a mount on the side of the skimmer. It draws water in through the weir, through the skimmer basket and then on to the waterfall.
I initially matched a Pondmaster PM-7 pump with this skimmer. That pump pulled enough gallons to run a small waterfall. The PM-7 pulls about 700 gph as long as you keep the skimmer filter clean. (FYI, I have since upgraded to a Pondmaster PM-9.5).

I saw your picture in the other posting of your current set-up and that waterfall looks like it runs a lot more than 700 gallons per hour. How big is your current pump? If you are planning to use this skimmer / pump combination to push your waterfall, you may want to use a bigger pump, like a PM-9.5 or even a PM-12.

However - this all leads me to some other questions. If you want to run an attractive waterfall, you will be turning over the water in a Rubbermaid 300 gallon stock tank several times an hour. Your water lillies may not like so much water movement!

How many gallons was your current (previous) pond before it developed the leak? Have you thought about reinforcing the walls somehow, and re-laying a new liner?

I cut a weir for a waterfall in my 300 gallon rubbermaid tank
I used a reciprocating saw and it worked out great. I do not see why you could not cut out a section for a skimmer.

Cool pond! Smaller EPDM liners are about the same price as the tank, are very durable, and you could make the shape anyway you want and maybe get a little bit bigger pond. Also you could get a bigger skimmer, one where the pump sits inside. Alot easier to maintain when they sit in the skimmer.

Good luck!

I really appreciate all the comments. Camperman, I believe my pond is currently only about 150 gallons, though at first I really overestimated it to be about 600, lol. There are so many rocks inside it that it might be less than that. The first year I had a rather powerful pump and extremely good waterflow down the falls. Everything I had read led me to believe the water lilies would not bloom, but they did. The next year, I had to replace the pump and got one that had a fountain. That decreased the flow down the water falls so as not to disturb the lilies, but a combination of too much shade and probably not enough fertilizer led to less blooms. Then about the time they were looking good, a raccoon tore the whole pond apart. It has never really looked good since.
I think I am going to go with the Savio compact skimmerfilter that will go on the outside and buy a pump that will fit inside it. I doubt if the one I am currently using will fit. The $ are adding up, but I don't have a lot of time to constantly be cleaning the pump which now lies on the bottom of the pond.
I took a look at a 100 gallon stock tank today to make sure there was enough flat vertical surface area in the top tier to cut through for this skimmer and there is.
Thanks again for the suggestions and advice everyone.
Sherry

The savio compact is an awesome skimmer, I have one too:) Make sure to get the 6" face plate and I wouldn't go over 500gph on the pump or the current might get a little strong for a 300 gallon pond.

Evesta, is the 6" face plate better than the 8"? I really like the way this skimmer looks and sure hope we will be able to fit it to the stock tank. The first tier is probably going to be a little short, but my son is sure he can make it work. I haven't found another external skimmer that would work, but I'm going to keep looking just in case the Savio doesn't.

The smaller face plate is for smaller ponds that have less surface area. Savios are super tough and great skimmers!

Oase swim skim is another option for you. I have one for my 3000 gal pond and it works pretty well. Just needs cleaned often due to the smaller size basket. It might be perfect for what your looking for.

billinipa - Thanks for the info. It looks like a really good buy since it includes the pump. I'm still hoping the Savio will work since I like the idea of not having any cords and hoses in the water, but the tank will be here in about 4 days and we should know then if we can make it work.
evesta- Do you think the 8 1/2" face plate will be too large for a 5 1/2 ft. diameter pond. We get a considerable amount of leaves and pine needles in the fall and a variety of spring seed pods for the lack of a better description. I can exchange it for the 6" if I need to.

Have I said thanks to everyone recently? My existing pond was put it 2 1/2 years ago on a whim...actually thought it could be done in less than a week while my dh was out of town. It ended up taking a couple of weeks. That was before I had heard of the pond forum. All knowledge I gathered the after the fact helped me create a really nice pond in spite of the rush installation. Now that I need to redo it, I want to take my time. Actually there are plans for a much larger pond elsewhere in the yard, but I want to keep a smaller one at this location just off my patio. HMMM...maybe a stream to connect the two??? Anyway, I know there will always be ponders out there to help with the questions I have.

The face plates are based on surface area not amount of leaves. The basket for the leaves is the same size with both and accomidates a lot of leaves. I would think the 6 would be better for a smaller pond. My pond is 19X7 and I have the 8 1/2. It clears the whole surface of leaves but sometimes it almost seems like the current is too strong, witch is probably more of my large pump then anything.

Somewhere on the savio site it should say what the recommended surface areas are. Have fun!

I looked at the diag again in your other post. The 300 gal stock tank. Will the salvo work on the curve of the tank? wil the plate seal against the hard plastic curve like that?

Depends on how big of a hurry you are in but I will upgrading my swimskim sometime this summer.

billinpa,
I held the face plate up to the small version of the stock tank and was able to find a flat surface big enough. Actually, in my drawing, I show the tank as round, but it is more square with rounded corners and since the width is about 5.25 feet and the length 5.75 feet, there will be plenty of places to put the skimmer. It should be delivered some day this week, so I'll see. The main problem is that the tiered sections are a little short, but my son says he can make it work. Otherwise I will have to find another skimmer. I appreciate the other suggestions.

evesta - Thanks for the info on the face plate size. I will probably exchange it for the 6 in. What you said make sense.

Sherry