I have the same tank and am picking up clowns next week, so looking at modding mine today to stop them jumping over the back I have 2 possible plans to reduce the risk either some egg crate and silicon sealant or some weir comb material.
However if it happens, don't spend hours trying to get them back - just raise the water level to aas high as you can get it without it overflowing on your carpet and they will swim over in minutes, then just lower the water again
Seffie x
ps perspex will work just fine - use reef super glue so that it doesn't look ugly