[Boolbar] If you put the doors up first, you can then shut them and therefore won't have so far to chase the mice. Also (if the mice co-operate) can the chase not be part of your workout? Could you persuade them to run at half-pace for the first ten minutes, then full-pelt for 15 minutes, then a cool down pace for the final ten? It would seem to be the organised thing to do.