Not allowing Simba to roam is the only thing that will protect him from other cats (and predators). Consider keeping him inside, only allowing him out on a leash, or building a catio (my cats love theirs). Other than coming home with scrapes, he's also at risk for fatal viruses that vaccines don't protect against like FeLV and FIV. Is Simba neutered? He's at an even greater risk to injury, illness, or death if he isn't.
There's really nothing you can do to keep cats out of your yard, and keep in mind when Simba roams he might be doing the same thing to your neighbors' gardens.
I should mention though that a cat is realistically not going to take a sapling. A lot of the garden damage you're describing sounds like squirrels hiding food, rabbits, or raccoons.
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Rachel Watsky
VP
Feral Freedom, Northern California
OR
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