Penny wise, Pound Foolish (Warning: R18 post)

I made a mistake 3 years ago when I first got Polo and Paula. I had decided that since I was going to get Polo neutered, there was no need to spay Paula. For one, I just thought that if one of them cannot reproduce, then my problem was solved. Secondly, neutering was a relatively cheaper procedure than spaying.
3 years on and Polo is now one of the timidest males of any species I ever know. Paula on the other hand, urinates all over to mark her territory, scratches when she's in a bad mood and NEVER leaves Polo alone. In fact, she's always seeking to hump him even though she's obviously not suitably equipped (ok. I can explain what she's really trying to do but not on a public blog)! And Polo gets scuff marks all over him because Paula bites him to keep him still. I'm making it a point to bring them to grandma's regularly for them to run around the garden there... but Paula inevitably catches up with the not-too-smart Polo and "gets it".

I blame only myself.