I train in Sambo and love doing heel hooks, leg locks, ankle locks and knee bars from the gurad, YES it is possible!
I wait for him/her to stand on one leg, then open my guard, hook the leg with my foot at the same I shift my body towards the leg. Lift the hooked leg, grab it and I got a BEAUTIFUL knee bar. If they twist their body to void the knee bar then I turn it to a ankle lock or heel hook.
[This message has been edited by Sambo (edited January 18, 2002).]