We had this at our Relay last year.  It was call the Amazing "Relay" Race!!  I involved the teams to come up with some type of game or challenge that the participant had to complete before they would recieve their next clue.  I found out ahead of time which teams were participating in the game, then I didn't make up clues, but I just had them go to that team's tent.  The thing is that not all the tents had numbers, so you had to know where the tent was.  It was fun!  Just don't do it in the middle of a hot day.  We did it at 11 in the morning and it was hot and there were running from one end of the track to the other and one of the teams had them eat a whole donut before they could get their clue!  They weren't feeling too well after that!  Good luck!!