Hardware cloth...

[duckncover]

how the heck do you cut it so it isn't pointy?

What tool do you use to make it so straight

 

[Teach97]

metal shears...they look like super heavy duty scissors...you pick a line to follow and get after it cutting close to one side...it isn't perfect but the idea would be to use trim over it to hide the edge

 

[monarc23]

after what teach said you can sand or file it down even more too

 

[Chicksdigit]

If you want it really smooth you can use a Dremel tool.