In the following video, Gracie Barra athlete and teacher at Roger Gracie Academy Lucio Lagarto teaches some tricks a good guard player can use to make things rough on opponents by sweeping or subbing with a footlock.
HAND IN COLLAR AND FOOT ON RIB TO KEEP OPPONENT LOCKED IN
The move starts with fitting the right hand into the right spot in the collar. When the opponent comes after you, it’s important that you place your foot precisely where Lagarto indicates—that way, you won’t cross the knee and get disqualified, nor will leave your opponent free to advance.
Learn from Lagarto, and derive your own lessons. What’s the main thing you learned, sagacious reader?
http://www.youtube.com/watch?v=Yr_uXYublB4