I had this problem and a solution!
Solution one;
I found these gel "stickers" that I just put around the viv. about 5 inches up, this means that the crickets get stuck to this and can be easily picked off by a hungry dragon. No "gel" comes off, and they or human can easily peel the crickets off but the crickets themselves can't pull themselves out. Hard to explain.
They don't leave a mark when you take them off the walls. They're non toxic, 100% natural, hard to get though.
Solution two;
Double sided sticky tape, stick this around the walls of viv, at a low height so easy picking for you and or dragons, and once finished with easily peeled off.
Cheap and easy to find. Best one.
-Rose, Zack, Izzy and Jess.