You can't prevent them, but there are strategies you can (row cover, timing) take as well as varieties of squash you can try instead. Peruse the many SVB posts here for ideas.
Take heart, you CAN still grow squash despite this dreaded pest.

How do I ensure they don't come back next year?

You can't. Use the winter to learn about them and how to protect the plants next year.

Dave

Here is a link that might be useful: SVB discussions

I had good success injecting BT this year. Though stressed and damaged (several got powdery mildew once weakened), the borers died and the plants recovered and are still growing and producing (although not as well as before). I caught them pretty early this year.

I'm thinking next year I may just start preemptively injecting the plants with BT.

I think especially for summer squash, the best solution is to cover them. I covered my yellow and patty pans with tulle netting, and they did great until they outgrew my cover. I uncovered them yesterday. After next week, I will probably inject with BT once every week as long as the plants stay vigorous. There are still lots of SVB moths flying around unfortunately (here in Texas we get around 3 generations).
The other thing I might do is plant another batch to put in the ground in early Oct. By then the SVBs are gone, and I have till late November until we have our first average freeze.

@CaraRose:you sure that is a good idea? It is like eating antibiotic pills before walking into the rain. This really sounded too pessimistic.

I got so tired of them squash things, mildew, etc. that I just pulled them the other day
sigh of relief !

I don't see it much different than spraying rose pride on my mildew prone roses before they get powdery mildew. It's a lot easier to prevent it than to cure it.

I have had the worst luck this year with SVBs. I didn't know what they were until it was basically too late. My plants were so stressed that they never produced anything. What I started doing after I learned about them was to search each stem, leaf, and flower every day or two for the eggs. I picked off the eggs and squashed them. That helped tremendously and my plants started to recover. But, then I went on vacation and the SVBs went crazy!!

Now that I know more about them I will try again next year. I'm going to till my soil really good to get anything wintering in it gone. I'm also going to start my own seeds instead of buying seedlings. Then I will start examining my plants VERY often right from the start! I haven't thought much about covering them up, but I may take that into consideration.

Here is a picture of SVB eggs! Hope this gives you some ideas. I'm in central Texas.

I still see no difference. I'm spraying the roses on the chance that mildew spores will land on it and infect the plant. The spray has a longer effective time than BT, obviously, but it's limited too, that's why I have to spray every 1-2 weeks (and failing to, I get mildew infestation like I did last year and beginning of this year when I got negligent about it).

Since at this point I'm positive my plants WILL get SVB. No matter how hard I search for eggs, I'm going to wind up with them. It's not a matter of if, but when, then at some point my weekly injection will overlap a point of time when they're too small for me to see obvious signs of them, but already inside eating, and kill them before they do too much harm.

I got to them with injections this year before they did enough damage to kill the plants, but they still did enough damage to hurt production and weaken the plants. Taking a preventative approach, I may be able to kill them before my plants are weakened. You do a series of injections up the entire vine, and the amount you inject is actually pretty low to fill the cavity in the vine. I only mix a cup full and after injecting six plants, I still have some left over that I usually spray onto my broccoli.

This post was edited by CaraRose on Fri, Sep 6, 13 at 12:18