Squirrel repellent

Last weekend I have an elephant bush destroyed by a squirrel, it was one of my prized elephant bushes, roots over rock, nice nebari. Since then I have killed 7 of them at least (air rifle). Today 2 more elephant bushes have met their demise, several more gnawed.

Is there any repellent that works? Or do I just have to annihilate them? I’ve work very hard on some of these trees. The elephant bushes seem to be the only ones affected, and they are in a garden with other trees, and vegetable raised garden beds but those haven’t been touched.