I used a tuning fork which, if you put the 'sharp end' between your teeth (bite it lightly), it rings in your head so you can hear over noise! Always used/use harmonics, even with a tuner. As my TC electronics dooby is used for guitar too I leave it on that setting then harmonics seem to work better.
Why do people always leave their clip on on the guitar for the whole gig? I think it makes me look like a complete noob so always take it off. Mostly I'll have something to step on on the floor anyway mind.
Didn't John Entwistle famously have perfect pitch then had to submit to tuning to Pete's harmonica? Must have been hell....