Hard.
Okay....now that's out of the way. Defoors grip is the way to go for running a 226 in my opinion. FWIW, that's how I shoot all guns now, after 15+ years on a 226. Some folks are in the "Just ignore it and don't worry about it camp", but I think that's the wrong answer IF this is a defensive tool. Absolutely, positively know the condition of your weapon at all times. I've seen tons of shooters on 226s not pay attention to this running the guns for a full mag....and then getting the superloud *click* when they wanted a bang.
Bruce Gray I believe came up with the idea of training with a band aid on the support side thumb as an index point for your strong hand thumb. During an Advanced Pistol class several years ago, Mike Pannone would not let me or my coworker leave the range until we fixed the problem, since we were stuck with department issued 226s. Had us do the "1+1+1" drill. All our mags, and the partners mags, loaded with 1 round. Just kept firing 1, load, fire 1, load, fire 1, load....did that for 60 reps while your partner was topping off the empty mags with 1 round each. Fixed the problem permanently for me. Glad I did it.
YMMV