Holy cow, what a week with the animals. A few months ago I took in a little stray, wild dog who was abandoned when her former "owners" (ha ha) moved away. She's come into heat. Yesterday I go outside to find my male NEUTERED dog tied to her. Today, same thing. My vet assures me he's shooting blanks, but I've never heard of a neutered dog actually mating; have any of you? Man, dog problems, goat problems--it's not a good week.

Lol, yep, mating is an instinct that is not always "erased" with a clipping :p

It is common for neutered males to mate with females in their receptive time. There will not be any puppies, but any such mating can lead to infections. I always warn people about leaving a female in season around even a neutered male for that reason.

Perhaps with a stray you have taken in not long ago, you can be excused for not having had her spayed yet. I greatly admire people that take in strays. I do want to urge you to keep an eye on her. Even if she is in a fence, other males will risk their parts jumping over the fence. Do not underestimate what she might do to get loose and go find another male. She will continue to mate with any male she get a chance to until her fertile time passes.