simplest way would be like
(inverted)sprite.rts is moving
every random(10000)+ 1000 miliseconds
sprite.rts move to position xrandom(layoutwidth) yrandom(layoutheight)
That would be for a single sprite, you could use a family instead, or even pick a random member.
edit:
Note if you have a lot of objects the pathfinding may bog it down a bit, if so just use add waypoint at position.... that is if your using rts behavior.