So, in theory and in law, multiple parties could have unregistered copyrights on essentially the same work and each could claim, without proof, that...
If we assume that the neighbor could buy a set of plans (become a licensee) and then hire the OP as a third-party agent to build the squirrel house,...
I thought "surely this can't be right" but apparently is. Maybe this helps sell their Driftmaster Fence(?). At any rate the fence adjustment process...