How to keep a cat out of my garden?

Try placing some bags with chunks of Irish Spring(original scent). Most Animals do not like the smell. You'll have to replace on a regular schedule as the smell wears out. I've also heard they don't like the smell of moth balls.

We've been using plastic forks for quite some time, every year we place them around each new plant until they grow large enough, once that happens we pick them out and store them away for the next growth cycle. In the past we've used popsicle sticks as they are much easier to get in bulk for less.

The popsicle sticks might actually be better for your situation. Good Luck.