I have engineer gobies (2- 10" long), A yellow-headed watchman goby, but by far the most creative tank architect when it comes to hardscaping is my tiger pistol shrimp.
(Actually I have 2, one in my 29 gal and the one I'm discussing now in my 6 gal nano). I had purchased a long awaited pearly jawfish and in preperation I had placed a new lava rock to provide a cavern as 2 other rocks had been claimed by the shrimp and joined by a tunnel. Unfortunately, the first day, the jawfish while seeking out refuge had backed into the shrimp's entrance...which I thought would be interesting but this thought was not shared by the shrimp as later that day I found the jawfish dead a few inches away with a shredded tail....I think from shock. So my son and I are raising oysters on his island property so I had placed a Pacific oyster spat in the tank before the rock. (Yes it's growing) I came home today and found the shrimp shoving the oyster away from the new rock! Apparently, it also wants to claim this property also as it has moved one of my rocks with the candy cane coral on it into an intermediary position between the 2! It's a strong little bugger. I just put an orange spotted watchman in today and I hope they get along...but the shrimp's a mean ole cuss....but so's the oyster. When the shrimp would push on the oyster the oyster would spit sand on the shrimp which would make him back away for a few minutes. Sorry about the quality of the photos, I only had my samsung phone...the new one's are much better. The last picture is where the oyster came from. Please expand the photos...they'll look better.)
(Actually I have 2, one in my 29 gal and the one I'm discussing now in my 6 gal nano). I had purchased a long awaited pearly jawfish and in preperation I had placed a new lava rock to provide a cavern as 2 other rocks had been claimed by the shrimp and joined by a tunnel. Unfortunately, the first day, the jawfish while seeking out refuge had backed into the shrimp's entrance...which I thought would be interesting but this thought was not shared by the shrimp as later that day I found the jawfish dead a few inches away with a shredded tail....I think from shock. So my son and I are raising oysters on his island property so I had placed a Pacific oyster spat in the tank before the rock. (Yes it's growing) I came home today and found the shrimp shoving the oyster away from the new rock! Apparently, it also wants to claim this property also as it has moved one of my rocks with the candy cane coral on it into an intermediary position between the 2! It's a strong little bugger. I just put an orange spotted watchman in today and I hope they get along...but the shrimp's a mean ole cuss....but so's the oyster. When the shrimp would push on the oyster the oyster would spit sand on the shrimp which would make him back away for a few minutes. Sorry about the quality of the photos, I only had my samsung phone...the new one's are much better. The last picture is where the oyster came from. Please expand the photos...they'll look better.)