Electronic – Soldered wires don’t last very long on PCB

That's probably because the wire isn't clean. Use extra solder with flux kernel, the flux cleans the wire (reduces any oxidation). The best thing is tinned wire, even older solder should flow up that wire easily.
Tinned wire is also easy to lay out on the perfboard: just hold it/heat it with your soldering iron, and the solder will flow nicely over the pad and wire.

Ideally, you should avoid finding yourself in this situation. Using appropriate connectors or atleast making sure you have enough room to comfortably attach the wires on the pads is a useful thing to do. You should certainly try to fix the problem more robustly if you want to produce or manufacture the thing.

For a one off thing, though, hot glue should work. There is a technique called potting, which using a different material, which does essentially what you imagine hot glue will do. Typically, potting is used to reduce stress at connector/solder joints and prevent cables from flapping around and so on. The potting material is better at doing this if the signals are especially sensitive in some way, since hot glue isn't a material explicitly chosen for it's insulating/dielectric properties. You should give it a go, though, for most applications it's probably insulating enough.