To continue to run an open tank what you can do is purchase a sheet of eggcrate from your local hardware supply store. eggcrate is the white plastic grating that is often placed under florecent light fixtures to difuse the light. Usually the eggcrate is made up of small 1" squares. You can use some heavy duity cutters to cut out the size of your tank and place this over the tank. Then to have the fish jump out they would have to get thru the 1" squares.
This is exactly what I have done to my 40 tall in my store. Keeps the fish in and the customers hands out. FYI
, eggcrate isn't the easiest thing to cut. I used a combination of tin snips and a box cutters to cut it to the correct size of my tank.
You may even want to buy two sheets just in case. The size it typically comes in is 2' X 4'.