Beer drinkers who are interested in a quick’n'dirty strap lock system for your guitar are in luck. Get two bottles of Grolsch and use the red rubber gaskets as strap locks. The advantage of using the rubber gaskets is that they are small enough to fit through most straps, but still do a good job holding the strap firmly in place. The soft rubber doesn’t damage or scratch your guitar. You also get a valid excuse to drink two bottles of imported beer.
I learned about this trick during the last SoP tour. I was in the rather precarious state of having no strap locks, but our guitar tech Hans heroically located two Grolsch gaskets and deftly installed them on my pink guitar. (I am not sure if drinking was actually involved.) These DIY strap locks kept my guitar safely around my neck, where it belongs. When I got home to Sweden and got out my guitar, I was happily surprised to find the strap locks attached; they are still serving me well today!