Covers tracks
Candidate: ... *Realises stupid question & thinks of cover up M: It's a trick question. You're hired!
Cover it in lighter fluid and throw a match at it: "WOOF!"
Your fence.
Anyone who can run, jump or swim is already over the border
Not enough sand.
Watching your mother-in-law backing up towards the edge of a cliff in your new BMW.
He threw them off their tracks.
A pedometer