Aren't Jawfish aggressive? I was going to get a yellow head jawfish a while back but heard nothing but bad things about them. Also I am looking further into the Engineer Gobies (Just wanted to do some extra research) and are finding that they are cool fish said:
Nope, they're a little protective of there 'home', and they are burrowers. They build a home in deep sand beds 3"-5", but they're really cute and have alot of personality, once they make there home they pop out and hover over it to feed. They can be pretty good excavators so you should make sure your rock is supported by either base rock in the sandbed, or maybe pvc to hold up the rockwork. Just anything to ensure it doesn't all come crashing down.
http://reefkeeping.com/issues/2002-03/hcs3/index.php