Guarding the Upline

Sectionals is this weekend, first game is against Chain, then against Six Pack.  Voodoo scrimmaged UT tonight, with us winning, though UT didn't play their best lines.  In scrimmaging I had a hard time guarding a throw and go handler (Mark) on the up line.  It seems the only way to defend is to make sure it doesn't happen - after it happens the defender is playing catchup / damage control.  I found myself just chasing Mark up the field as he essentially did throw and go's with various players.  The way I understand the rules is that you have three steps to stop after a catch, so as long as you throw it within those three steps without changing direction it isn't a travel.  Mark is also left handed, so running off his backhand plays off a force flick. J?