Rips and Tears in the Mesh
If there is a hole in the screen, you can even patch those up easily. However, if the diameter of the hole exceeds 3 inches, then you may have to replace the screen. This may take a long time, depending on the kind of mesh you are working with. Also, if it is a fiberglass, you may need to replace it, as it is tough to repair. Here are some instruction.