I have a Fluke non-contact voltage tester and a Snapit outlet tester in my gig bag. Some place just have bad wiring and the only protection is that the testers let me know (and I pass it on to the rest of the band). Sometimes, like at a pool party we played, you can let the home owner know they have a problem and request to use different outlets. Other times you have no choice but to play and be careful.

I've used the cap and resistor protection as described in that article. Keep in mind that a Telecaster's metal parts and metal humbucker covers and other parts directly attached to ground will still be hot.

It also won't protect you from the amp's chassis and switches being hot.