Is there a practical solution to squirrels stripping bark from pine trees?

On pines, the squirrels rarely make it past the bark to the vascular system and therefore they are mostly just a visual nuisance. On palms, a smooth metal collar is put around it, but this cannot be used on trees, as over time the tree will girdle as it expands in girth.

If squirrels are getting past the bark layer, this would be a cause for concern and make an appointment with an Arborist.