There are many solutions:
- double-side-glued 3M adhesive tape: easy to handle, and what is used at most factories to glue new pads.
- cyanolate (contact cement) for small repairs: typically around the handle
- epoxy resin
- (my favorite) the new class of glues: "MS Polymer" (see
translate.google.com/translate?hl=en&sl=de&tl=en&u=http%3A%2F%2Fwww.wikidorf.de%2Freintechnisch%2FInhalt%2FMSPolymerKlebstoffe&sandbox=1 ). They offer a lot of advantages, and are solvent-less, which means they do not try to dissolve the board surface for providing adherence, meaning they are easier to sand away if you decide to remove the pad afterwards. Plus their are safe (no glued fingers)
I use "UHU Max repair" which I find quite easy to use: rather quick to harden, but allow a full 5mn free repositioning, only need to apply on one side, and glue as soon as applied, lessening the need to apply pressure on the whole pad while setting.