Hello Kat,
How do I keep my neighbors cats out of my garden? I've tried cayenne pepper with some success, but it loses its effectiveness quickly, and I don't know if it will spice up the crop! Kitties seem to be drawn to the loose rich soil in the garden, and I've heard that cat feces can be bad for human consumables.
I've resorted to placing thorny twigs around, but that is temporary and time-consuming. Can you help?

Well, this can be a thorny problem! You're right, cat feces can leave parasite eggs in the soil, not a good thing. Making your garden less attractive to the cat is probably the way to go. The thorny branches sound like a good idea, but might make it hard for you to get in there to weed. Try this spray repellent I found in a book: 4 Tbsp. dry mustard, 3 Tbsp. cayenne pepper, 2 Tbsp. chili powder, 2 Tbsp. ground cloves, 1 Tbsp.Tabasco sauce, 2 quarts warm water. Mix all ingredients together and sprinkle around the border of the garden.(courtesy of Critter Control and Pest Prevention by Jerry Baker). You can also buy spray cans of animal repellants, or put straight vinegar in a spray bottle, but any of these will degrade with time and rain, so they are labor intensive.

Adding a thick layer of mulch, like bark chips or even white stones, could make it much harder for the cat to dig in, and discourage it. Another idea from Jerry's book was to lay a two foot wide strip of chicken wire around the edge of the garden, which cats don't like to walk on. You can even sprinkle seed of a low ground cover (like creeping thyme) right over the wire so it will hide the wire when it grows.

Bordering your garden with an electric fence is probably the surest way, but would take some materials and time to install.
Good luck Pazinmusic! Let us know if you have success.