I've just got some Bondic which is a kind of viscous glue that only hardens when UV light is shone upon it.
You get a tube of the glue and a small UV light source.
It's pretty good. I use if to strengthen otherwise weak soldered joints especially where flexing happens, e.g. affixing jumper wires to battery packs.
I wondered if anyone knows of a similar but much cheaper version of this UV bonding glue?