The WD-40 stuff is something like 2-40-D or something very similar. I always get kind of mixed up but I THINK it's pretty toxic.
I have mountains and mountains of poison ivy. I have poison ivy creeping over here from the cow field across the road

--- I have huge and ancient poison icy vines creeping into some of the trees

--- I have poison ivy starts trying everywhere.
For SOME of the poison ivy, I've found the only thing that works is Brush B Gone --- this has worked best on the very established poison ivy I have --- the stuff with an extensive root system.
For SOME of the other poison ivy (the stuff branching off from an established poison icy system), I get dried Round Up, mix it up triple strength in a Mean Green Super Strength Cleaner spray bottle (the cleaner is great AND cheap, and these are the best and most accurate spray bottles I've ever found!) and I whoop on it!! :yeeha:
Vinegar and salt work great on fresh starts not hooked into establsihed root systems. Bleach, eh. Don't bother. Much to my disappointent, it only seems to burn the leaves, but does nothing to eradicate the poison ivy.
If your husband can, have him dig around the base of the fence to see if there's a poison ivy root system down there. If so, he needs to pull it out.