Each end of the snap has two pieces, you punch a small hole in the material and put the bottom end of the snap on the inside of the vest and push the male end threw, then take the other piece of the snap and place it over the same male end, then smash the male end down with a tool usualy comes with the snap kit, and it wont go nowhere.
Just make sure that you clean your syntra with alcohol and use a blowdryer to heat up the velcro a little ''dont over do it. The heat will make the adhesive on the back of the velcro very strong to stick on your syntra . It should work..
loctite super "future" glue from wal-mart is fantastic. I've used it on batman costumes before to glue the latex body pieces to teh wetsuit i'm wearing, and it keeps them there no problem. Strong stuff and may be just what you need. Just dab it on the back of the velcro.