I've seen people using washers and concrete screws as straplocks and was thinking of the same.

Maybe not concrete screws but was going to try the washers and screws, and wanted to replace mine in my current RG guitars.
Will I need to get longer screws as I will have washers in there that mean for the screw to stick out more?
Washers and a good screw is a great solution if you never need to remove your strap. If you can find #7 Lathe screws, 1-1/4" they work very well,
as they are a nice size to upgrade for security, and have a nice wide head that will hold a good sized washer.

Below is a #7 lathe screw compared to the often pathetically small regular stock OEM strap button and screw.
Always a good idea to use a nice big felt washer too if you can

Another option is if you get 3/8th inch I.D. (inside diameter) washers, they often fit right onto the typical space capsule type strap buttons from behind,
but the hole is too small for the larger outer end to go through, from here you can figure that out. Sometimes they need just a tiny bit of round filing to fit
over the small side of the strap button.

so you pull the button, pop on the washer, install your strap (from behind) then reinstall the button. You can probably figure out how that works.
very secure.

I would worry that with what I think you have planned is you may have a strap that is simply being suspended by the threads of a screw. eventually that will shred your strap unless you clamp it really tight. I've done some experimenting with other strap retaining ideas - this is one of the better ones I have found...
you can buy these small suction hanging thingies four for a buck...

Then you do this with your chosen screw and a finishing washer.

Better yet, if you can find some old jean waistband buttons this is a pretty good solution too...

Last edited by Well-Hung at Dec 18, 2016,
Just get the Fender rubber type washer.. put your strap in then the rubber washer and the guitar should be stable.. I don't know how you wear the guitar strap so there is no guarantee it will not fail.. you could always buy lock-it strap. Planetwave has it but I don't like the big bulky plastic mechanism.
I have Washburn guitars 'Maverick Series' and bass 'Bantam Series' and a few pedals and amps, but man I wish to have more patience and drive practicing my playing, if it's equal to the modding itch, then I'm golden.