Regressing potty trained 3.5yo?

First I should say there have been no major changes, but we are planning to move in 4 months and I really won't be able to deal with this then.

My 3.5yo has been potty trained for almost a year. Lately he has been doing the potty dance, but then when I tell him to go potty he insists he doesn't need to go, but then goes in his pants. He's not doing full out peeing in his underwear, more just like leaking a lot, but enough to get his underwear and front of his pants wet (but not soaked). I have tried putting him in time out, he does have to take off his pants and underwear each time and put them in the laundry and help me get new ones. I have also tried insisting he goes potty, but short of physically taking off his pants and sitting him on the toilet he refuses. He's getting plenty of attention otherwise, no less than usual certainly. Its just like he wants to hold out and not go so he's not interrupted, but then he can't quite keep it in. This is getting to be a real problem whenever I want to leave the house especially (he stays home with me). Any insight or ideas?