I do not personally pocket carry...just a pet peeve that I hate having Anything in a front pocket.
Regardless of my proclivities, the above info on pocket holsters is 100% accurate. Any carry method, be it pocket, purse, holster, whatever, should include a holster that completely blocks access to the trigger unless the gun is drawn.
It's even more important with pocket or purse carry because your trying to extract the gun from a confined space and doing so under duress.
Remember that when adrenalin hits the blood stream, fine motor skills go out the window. Clutching for a hand cannon in close proximity to tender spots like the femoral artery and the previously mentioned cahones can result in fatal consequences for you and leave you completely at the mercy of your attacker.
Definitely invest in a quality holster. Training would not be a bad investment either.