Hi Cheryl,I live in Albany so I understand the type of ground you could be talking about.
Firstly,your trees will not want to be inundated,ok for a day or two but not much longer and that includes deciduous.
Choosing the correct species will be important. Mt.Barker is hot and very dry in summer[so how are you going to water them if you are working in Perth?] and quite cold in winter.Lots of cherries come frm Mt B. Put in a dam as soon as you have aproval!!

Is your soil heavy or sandy? If its wet sand it could mean that it is also acid. I would recommend you treat yourself to a pH kit and do some readings then take the appropriate action.
As far as the Kangaroos are concerned,I would advise strong wire mesh around 3 or 4 star pickets on every tree.Good strong Jarrah stakes will surfice.
If you have power on the block, consider an electric fence around the whole thing with 2 wires, one at belt high and the other about 20cms off the ground. I assume its already fenced but the above will help. I hate to say it but be prepared to have your heart broken a few times with the roos.
The other thing is to go and talk to Bill Hollingworth at Bandicoot Nursery just south of Mt B on the Albany hwy. He will advise you best as to the native plants from your area that will succeed.
Good luck and I am sure you will be thrilled with your new enterprise.
R

Thank you so much, follicle, I have seen that nursery, why it didn't occur to me to make it my first stop I don't know. We will do that as soon as we can. Also an excellent idea on the PH kit, will get one and test several areas. We were down at the block in Nov and again in March, there is a hole there that had water approx 1' down in Nov and approx 3' down in March...though that is hard to tell exactly, more a guess by the sound of the frogs plopping into the water. I think there was some water in the "creek" each visit. There is an old fence there, we are hoping it will do. Now I know this sounds silly but I don't really want to fence the roos out, I like them just want to be able to grow some things they dislike.
The vendors have planted some trees down in the very low area and most have survived without summer water, one reason we liked the block so much, we are willing to put up with a lot of water in winter if we can have a little in summer. They even have some pot tyres with plants in that have survived, mostly Geraniums....hm...maybe the roo's don't like them, at least something I can put in then...:) Hadn't thought of a dam, will look into one as opposed to a bore. Our land is loam over clay according to the chap at the Shire that was kind enough to pop out and give advice re septics. I am thinking it may well pay us to pay Bill to have a look at it and advise us, may well save us a lot of time and effort in the long run.

Once again, many thanks, all good advice.

Cheryl.