The short answer is you can't. We have a very substantial homegrown Hazel. Everynow and again it bears a heavy crop of nuts. We normally have no squirrels, but in nut years they find us out. They shove those nuts everywhere, not just in pots. They really are natures little forest builders! Put there for the purpose of planting nuts for fun. One solution is get rid of your 'little nut tree' or pull em out, when found ,as I do.

I use cayenne pepper. I works really good on slugs

I put stones on top of my pots and stick canes in until they get fed up with me or put my garden fork and trowel on top of pot until they grow, but whatever we do they are smart little b's !!