You'll notice that the threads of the barb is gone. I used the ring saw to remove them. Takes about 5 min per barb. Ring saws are great, but you never wanna break the ring, it costs 75 bucks to replace, because it's a diamond impregnated metal ring.
All I did to secure them was take my Ace Marine Epoxy, and let it setup for about 10min, to make it less runny. Applied it to the barb, and pushed it on. I drilled the hole out with a 1/2" spade bit. Which makes the hole too small for the barb to fit through. So I used this conic "hole widener thingy" to ream out the hole. I would just keep doing it until the barb would just fit through with some force.
So basically, the barb sticks through, but the hex part of it sits on the back of the plexi. Where the epoxy is.