Personally I don’t like strap locks that are on the market. I’m not into the idea of anything separating me more from the instrument, especially when it’s more metal. They rattle and sometimes even resonate. I’ve also found that straplocks strip strap button holes. This led me to research some alternatives. There is an old trick of using rubber washers from Grolsch beer bottles. If you put your guitar strap over the strap button and then place the rubber washer over the strap, it will hold the strap on for most uses. If you have intentions of swinging your guitar around your neck and/or doing backflips onstage you’ll want industrial strength strap locks. Washers will not cut it. For most modest applications the washers work like a charm and won’t strip your strap buttons.
I use thick leather straps because I find them more comfortable over long playing periods. The Grolsch washers are a bit too thick for the Levy’sstraps I use. They don’t lock into place as securely as they do with a thinner strap. This led me to search for a better alternative. I made a trip to the hardware store to look for a slightly thinner rubber washer. I found HillmanWashers. The 3/8 x 7/8 x 1/16 Rubber Washer was a perfect fit for a wide thick strap. $7. for 40 washers is a steal.
Using washers doesn’t mean your guitar can never fall off if you’re not at-least a little careful. It does prevent straps from coming off while bending over or putting guitars on and off. They require NO modification to your guitar or strap and cause absolutely no harm.