feline overpopulation

We like to have a couple of cats around to help keep rodents and snakes away from the house, but they have a way of multiplying until we have a real cat population problem. Currently, we have nine felines hanging around eating expensive food and making a mess. I've been tempted to give them an anti-freeze cocktail some evening, but I don't like killing animals so I bought a humane trap. I brought it home this morning and within five minutes of baiting it with a bowl of cat food we caught one. I put the trap with kitty in the back of my truck and took off for Proctor hill seven miles away. When I opened the trap, out bounded the cat as fast as he could go across the meadow and into the woods. I thought I heard him crying, "yipee, yipee", as he ran. I could be mistaken. He'll be happy. These cats have been catching a lot of moles, mice, and rabbits at home so he has the necessary skills to make a living in the wild.

Now here's the problem. Lizzy the wonder dog wont let any cat near the trap . She stands guard and chases away every cat that comes near. Has she been overcome with altruism and can't stand the thought of those kitties living a life in exile? No, she wants the bait for herself. She's already set the trap off trying to get inside to have a little snack. I may have to pull her out by her hind legs if she gets stuck. I guess I'll have to do my cat catching at night when Lizzies in the house sleeping.