When it comes to stuff like that, dogs and cats are idiots. I've seen mine bypass fresh, cool water for stale, gross rainwater that's been sitting for several days.
Without knowing all the levels in your pool it's hard to know, but it is best to keep them away from it. Of course, this may sound cold, but if they are older dogs, nearing the end of their span, you may want to just let them enjoy themselves.

Just remember: Dogs and cats are permanent residents. They live their entire lives out with us. Children are long term guests. They move out and on...hopefully!

(as the father of 2 boys, and servant of 2 dogs and a cat who thinks he's a dog)

Carl