For the cats---bamboo skewers sunk into the ground. Leave an inch or so sticking up so you can see where you put them. The cats will poke them, hopefully very gently, with their paws and not venture further. I did this in my flower bed and the cat problem was solved.
Wish I could help with the ants.

Yes, pongee sticks for the cats. I use old rose canes cut down to a manageable size. I also put bird netting down before I plant seeds, then mulch. Samcat hates the bird netting.

Water your garden and watch what happens with the ants very carefully. That's the best way to find the nest. What you do then is up in the air-- I have not found an effective organic control for the ants so I tell my husband about them and look the other way. I don't know what he does, but it works.

Good luck.
Renee

The only thing I've found that keeps the ants out of the vegetable garden is a vegetable safe pest dust, dusted liberally all over the ground around the plants -- I try to avoid the plants themselves because of the bees.