Are supports for spot lights required?
A lot of outdoor light comes with a stake or something to stabilize it.  I have ran a lot myself and basically I have two rules.  Run all of your wiring through PVC all the way up to fixture.  Second, if it doesn't come with something make your own stake.  If this thing is just a rock with wiring sticking out I would get some thick wiring, glue it on the bottom and stick that in the ground like a fork.  For more traditional type of lighting we put half cages over them but since this was made to look like a rock that would probably kill the aesthetics.