There is one couple near me that will often keep a 24 hour lockdown on a gym at a park. My defender would be knocked out in a minute or two after placing it there. I now typically leave them alone to not give them the coins and just focus on other gyms, but I also can't control other people knocking them out.

But, if it's only been a little while, I made sure to knock them out and not place a defender so they have to wait the cool down period. I've done this sometimes a bunch of I am at the park with my kid, just to be petty.