it's hard to suggest this without seeing your letters, but maybe punch a small hole at the top of each letter and use a thin wire thru one end of the letter and the other end of the wire thru the netting.
As far as glue goes, when I need a super sticky strong glue ( http://store.scrapbook.com/h-c605204.html)I use Memory Mount. I use a toothpick for small things like rhinestones and gems and they never fall off. Or I use a tiny paint brush for gluing small fonts.
Also if your letters a big enough, you can poke a brad thru and adhere them that way.