I made the sad mistake of allowing my very large, rambunctious oranda, to get stuck in-between a statue and tank wall, due to not having enough space for him to comfortably fit his body.
One morning I woke up to find my beautiful Sumo lying upside down in the corner of his tank, pinned between the tank wall and a statue! I was mortified! During his struggle, he had managed to rip his tail and scrape off several scales, as well as scrape the underside of his belly. I had no idea how many hours he had been in that position, or how long he had to struggle. When discovered, he wasn't even moving.
I screamed for my husband, who came running, and moved the statue so he could free himself. Although Sumo swam around as if nothing had happened, I knew he had to be shaken and stressed. I moved him into a 20 gallon hospital tank for several days, salted to .1% to relieve him of any pain his scrapes might had caused. He did sulk for a few days, although continued to eat.
Once added back to the main tank, of course I rearranged his decor as to minimalize any further mishaps. I have seen him practically get his little head stuck in-between the river stones and the filter intake tubes, so I am constantly arranging and rearranging things to keep him safe. Although his tail and scales are healing quickly, I will never forget practically having a heart attack upon discovering his accident!
On the same note, over a year ago I had a baby red cap oranda that got stuck inside of a faux barnacle decoration, after trying to swim through one of the holes that ended up being too small. Luckily, I had been watching him as he did it, and was able to remove him safely. Of course I immediately took out anything that he could potentially swim inside of. It was that day that I learned not to put anything in my goldies' tanks that had holes in it.
I am constantly learning what I can and cannot get away with, and each day lean more and more towards nothing but bare bottomed tanks and large river stones placed strategically along the bottom.