greater peach tree borers (repost)

I posted this under Fruit & Nut Trees and it says it got moved, but does not say where and I cannot find it anywhere now so I'm reposting...

Both of my peach trees died after being infested with borers, and now I just found them in my nectarine tree. They had already been declining and I had found borers before but I couldn't ever do much about it. I poured sevin dust around the roots, sprayed with dormant oil when appropriate, etc. My apricot tree is adjacent to the nectarine, and there is a cherry nearby, Neither of these two show signs yet but they are some of my healthiest trees so I want to do everything possible to protect them.

Any advice?

From reading various articles, I found the following suggestions:

- spray, spray, spray, to kill the adults. Because of a two week period of heavy rain during first cover, I missed a spray or two this year. The apricot I sprayed minimally because it isn't mature enough to fruit this year and showed zero signs of any disease, probably a mistake.
- treat trunks and roots with insecticide when planting. Too late for that now, but any specific details on this for when I replace the dead trees next spring?
- dig out borers with a piece of wire, but this comes with a warning that you are likely to cause as much damage with the digging as the borers do themselves.
- place PDB (paradichlorobenzene aka "moth ball crystals") in a dirt ring around the trunk. I haven't been able to locate these at any store or even online anywhere. From what I've been reading it doesn't sound highly effective. If anybody knows where to get some in reasonably small quantities I would love to hear where.