Trying to hang my paintings or what another fell!

Today I picked up my hubby's hot glue gun and attempted to hang my paintings.  Now if you have followed me before i have mentioned that I do small canvases.  Most of them are about 3X5 and are maybe a half inch thick.  Because they aren't on the box style like bigger canvases I can't just twist in hooks or hammer in tiny nails to hang them.

I tried to find frames at the dollar store but they are just too thick for what they carry.  Now I could go to Michael's and pay for professional framing but come on we are talking my little paintings and no matter how nice they turned out I can't afford to pay more than a couple bucks to do this.

As you can see they are not really that big.  Now what I tried was taking the glue gun

And attaching the little brackets directly to the back of my paintings like so

Well this method worked, for a few hours.  They looked really good up on the wall but when I was working on a short story I hear a crash.  The first of my attempts at hanging had fallen down.  Okay one I could expect, figuring I just didn't glue it good enough but well.  An hour or so later bam, second one falls.  So it is obvious that hot glue is not going to hold the hooks onto the paintings.  I am going to have to find a new method to hang my art.