My Dog Has a Frustrating New Hobby

I found out over the weekend one of my dogs (Koda), has a new hobby, and it's driving me nuts. His new favorite game to play is collect as many shoes as possible, flip flops included, and taken them outside into the yard. I am counting my blessings that he isn't destroying the shoes in the process, but it's hard to remember that after finding six random shoes outside.

What I find odd is that he hadn't shown this behavior until just recently and he is four years old. It could be part of the transition of adding a new dog (Gypsy) to our home or maybe he just has a new hobby. Either way I have to find a way to eliminate this behavior, it's going to start with not leaving the back sliding glass door open for him to take shoes outside.

What unusual behavior habits does your dog have?