I have just about torn every plant out in my tanks at one time or another trying to catch a fish.
The 2 net suggestion is good, another is using a clear plastic box and herding the fish into it and pulling it out of the water.
I've not built a fish trap yet, but I'm about ready to. From what I understand, you take a small clear plastic soda bottle, cut it off several inches down the bottle, then invert the top into the bottle, and staple it in place. It's harder for the fish to then swim back out than if you leave the bottle intact...place bait in it and put it in the tank. I guess this assumes you are wanting to cahtch a small fish.