There are a few options..
Make an outdoor enclosure for them.
Get a tie out, and put your cat on it.. use a harness though.
For me, I have an 8 ft tall vinyl privacy fence, so one of my cats who is extremely fat and short can't jump it. So he stays in the yard. However, the other cat, who is tall, and slanky can clear the tank with no issue. He however doesn't go outside my yard. I'm lucky that way.
and they are both neutered, so they don't increase the population.