I have problems with squirrels, as well. One has dug around a potted camelia and I have no idea why. I've used bird netting on some of my flowering shrubs to deter deer. You might try this on your shrubs. Bird netting is very light weight and won't weigh the plants down.

He chopped off your nandinas because he knows they are invasive and choking out the native habitat plants he depends on for survival. Yuk yuk yuk Oh I couldn't help myself sorry.

I had problems with squirrels digging up bulbs. I started putting out water for the birds and the squirrels stopped digging up the bulbs. Maybe that's what's happening with yours.....they are looking for water. try leaving out a dish where they can easily get to it if you don't already have one.

You can put pieces of window screening in your flower pots to keep the squirrels from digging in them. (Works with cats too!) You can buy a small roll very inexpensively.

I think my yard is a paradise for the squirrels. They drink from my bird bath, as well as the fountain. They dig up my bulbs and plant acorns in the many containers I have planted. Normally they are more of a nuisance than anything else and lots of fun to watch. This is the first time he got hold of a shrub. And, by the way, this nandina domestica is the firepower one that gives this particular bed color, not the invasive kind.