I have 3 cats, and they are all indoor only cats. It's for their own safety and the safety of our surrounding native wildlife.

Cat runs are fantastic, we have one that stretches the length of our house. You can also purchase or make portable ones, and they dont need to be attached tothe house.

But for the topic at hand, yes the citris idea is fantastic, and often helps. Also the squirt bottle will do great too. You can also buy these spike things that dig into the ground (can be used in lawns too) so the cat can't lay down on them...Or you can try purchasing a lot of skewers, and placing them randomly throughout your garden, the cat will be annoyed all the pointy things and not being able to find a spot to lay down.