Let me know if this scenario sounds familiar. You've got a Pokemon GO gym battle within easy walking distance, and you've visited it many times. Maybe you've even dropped one of your Pokemon there to help defend the place and reap the benefits.
Inevitably though, one of the other teams always comes and beats up your squad, flying its colors proudly. And since the Pokemon they leave there are impossibly tough, there's not a darn thing you can do about it.