Hi Digee,
I've had a
yellow watchman goby and
tiger pistol shrimp in my tank for about a year now. They are a lot of fun to watch. The pair have constructed a very elaborate maze of caves underneath the rockwork in one end of my 135 gallon reef tank. So far, I haven't had to deal with any rockslides!!! (Fingers crossed).
Benefits:
1. Cool to watch symbiotic relationship
2. Keeps the substrate stirred
Risks:
1. Rockslides
2. Shrimp (and fish) may decide to take up residence in the back of your tank. In this case, you will probably almost never see them.
The pair have been pretty low maintenance for me. I got lucky and they decided to dig front and center. The goby will dart out of the cave and grab mysis shrimp or flake food. I usually drop a couple of shrimp pellets in or near the burrow when I feed and the pistol shrimp will greedily retrieve them.
Wish I had a picture to post, but these guys have so far eluded my camera!