I usually have some task to complete before the season starts, and I usually go right down to the wire before getting it done. This year I'm working on a collapsible marten box for one project and designing a wolverine proof marten set for another project. What's on deck for you?
Concrete or steel! I'll post when done but it's not about durability but rather using the weight difference between the two species. I'm using a pole on a pivot point that will support a martens weight but pivots downward when a wolverine tries to climb it. Another prototype uses a slim upright sapling that a marten can climb for access but will bend over for a wolverine. My final model uses a piece of binder twine hanging down from elevated marten box with small dried spruce branches attached to it, again supports marten but wolverine is too heavy.
I'm leaning towards the pivot as it resets itself after a gulo messes with it while the other two could be made inoperative when a wolverine is done with them.