Why do cats come to visit my two spayed female cats?

pezbemine asked:

I have two female cats; they are both spayed. Every once in awhile it seems like every cat in the neighborhood comes to visit them. One of our cats, Kitty, also gets in the habit of peeing on things inside the house during this time. She doesn’t do anything else that makes it seem like she’s in heat. Even though they’re spayed, might one of them be attracting other cats? Is Kitty marking her territory? Any suggestions? I can deal with the cat visits but not the peeing.

Nasty Cat attacks