L.S.
Truthfully, when mine did that and I had had enough, I spanked him for being defiant and disobedient. It only took one or two spankings for him to get it under control. BTW, there were no issues other than him not wanting to go or being lazy. He just didn't want to stop and go. And he was to big at 4 1/2 to be acting that way. He even pooped on the front porch one time he had waited to long, because he knew if he dirtied his pants he would get in trouble with a spanking. As long as there is no problem other than them taking care of business, I guess you have to decide what you are willing to put up with. And how you want to handle any problems. I think at some point as a parent we have to say enough and have consequences that are very uncomfortable for them to stop the offending behavior. Anyway, that worked for us.
Good luck,
L.