Temporary Fencing

You will not stop them. If the fence is climbable the cats will go over something 12 foot high, especially if you have just tilled the land to provide the ideal toilet for them.

Probably you will also get suggestions for cat deterrents. Guess what? Yep, none of them will work, except maybe the shotgun or the anti-freeze mixed with cat food.

Maybe a high-power water pistol and have fun squirting them?

How wide? Netting stretched over the top?

nib

Neither of those is a deterrent - They're cat killers.

Lion dung used to be a suggested deterrent, but who has lions around?

I suggest chicken wire loosely laid over the surface - makes it very difficult for cats to walk over. It might also stop birds pecking at the new plants.

I doubt if the OP intends to sit out there 24 hours a day. Cats don't keep fixed hours, and are just as happy to be wandering around at 4 AM as at 4PM.

Fruit cage?

But they do learn!

Wrong. A cage with a top and a door for him will certainly stop them if done properly.

But perfectly possible to have a top for it.

Or a dog.

The learn to avoid but it doesn't stop them at other times.

You need a fruit cage. It is about the only thing that will work.

In order to outwit you. I cannot understand why we don't hear cats laugh. They always want the last one.

I put gardeners fleece all over some re-seeded patches of lawn to stop the pesky pigeons from eating not just the grass seed, but all the new soil as well !. Must have been all the tiny bits of gravel mixed in with the soil (those 40 litre bags at the garden centres) that made it so attractive.

Scattered some 30mm cobble all over the fleece to hold it in place. Very effective, the new grass even grew through the fleece in places.

Zoos sell lion dung for just this purpose. No idea if it works, but it's certainly available if you want to try.

Mike