Porcupines like eating plywood and wood materials embedded with salts like those from the handles of yard tools that become soaked with salty human sweat. Thiram is registered as a squirrel and rabbit repellent and may incidentally repel porcupines. This material is sprayed or painted on the plants subject to damage. It must be renewed occasionally to remain effective.
Common wood preservatives may repel porcupines when applied to exterior plywoods. Avoid using wood preservatives that are metal-salt solutions. These will attract porcupines.
But it is important not to expect too much from repellents. Frequently they don't meet user expectations.
Resources: (online)
Porcupines
