Here are 2 of the solutions for a bow front tank that I have done in the past. I just recently sold my little bow front, so I can't show you how they look on a tank (not great) , but they are effective for keeping your fish in!
This first one is nothing more than a screen cover with an extra piece of plexi added to the front to fill in the 'bow' area. This was 1/4 plexi and it is relatively easy to cut with a jig-
saw. Best with a variable speed jig-saw and you need to cut it slowly, but not too slowly or your blade will get melted into the plexi. Do wear protective eye-wear if you try this as the pieces of plexi are extremely hot as you are cutting!
This is (obviously) nothing more than a piece of egg-crate used to fill the 'bow' area and the pond netting is attached using cable ties.
This could also be use to create a cover for the CORNER tanks that are so difficult to cover!
**a note about using egg-crate alone. IMO it's an awful idea as way too many fish can fit through egg-crate. I watched my Royal Gramma sail right through a piece of this. If you only have very large fish, then ok, but do also keep in mind that egg-crate severely cuts down on the amount of light getting into your tank!