you could have a square plastic container like thing attached to a handle and at the bottom you could have it filled with holes like a strainer. then you could have a little hinged piece on the bottom without holes with a layer of silicone around the edges to that when you caught the fish you could snap the bottom on and itd be waterproof so you could catch your fish without ever taking him out of the water. of course, nets get into those little hard to reach areas though.
or you could have a plastic square container completely filled with holes like a strainer and have another slightly larger square container that you could fit snugly over the holey piece once you have caught your fish.
with my O, before i switched him to his new tank i had a plant pot container that had a drainage hole in the bottom. my O went in there whenever he was in a "sulk", so i just siphoned out some of the water(like i was doing tank maintenance) and picked the container up once he went in it. it was easy and i could just stick my thumb over the drainage hole so it was still filled with water when i transferred him.