I'm making an electric guitar made out of mahogany with a spalted maple top. The template is a les paul. Anyway, I was told about inlay stickers, and since I'm new to guitar building, I thought I'd ask: If I install inlay stickers on the fretboard, would they peel off too easily? If so, how could I better secure it onto the fretboard?

I put these on my first build (see sig.), although a different brand. They're on nice and securely and I can't see them peeling off any time soon. Just make sure your fretboard is clean before you apply them.

And come back and show us build pictures.
yeah I've used those stickers once or twice on my Gibson Sonex. need to order again actually. easy on/off look good. no complaints on them. have iron crosses on my RR320ST been there for a bit no problems. yeah no issues with them peeling unless you mess up placing them the first time you apply. like many stickers loose their adhesive if you put on/peel off. the crosses on the RR have been there close to a year probably as I built that guitar last Xmas and have used it for gigs and practice frequently.
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I put some skull & bones inlay stickers on my Ibanez last year (a little out of the ordinary for a country band, I'll admit, but it keeps people guessing) and they're still there. Haven't had any trouble with them peeling at all and I sweat a lot on stage. They even handle the sweat with...well, no sweat. Easy on and they will be easy to change when the time comes.