The easy answer is:
(send theGuard:setMotion(Wander))
or
(Guard:setMotion(Wander))
where theGuard is a pointer and Guard is an instance, or something like that. I forget the technical terminology. ^_^ However, when I tried to set up it, I noticed a small issue. You'll want to set up the looper as well:
(send theGuard:setCycle(Walker))
(Guard:setCycle(Walker))
Otherwise, he "floats". XD
The more difficult answer involves writing your own "wander" class, but that's a bit beyond my scope at the moment. ^_~