In an urban environment let me reinforce what I firmly believe: if you carry a gun, also carry an easy and quick to deploy sheath knife. The two are very complementary and cover a lot of vulnerabilities of a gun or knife alone.
Second: do not pat. Robbers commonly know that people carrying an uncommon valuable (to them) often pat it underneath their clothing to give themselves confidence it is still there. This includes wallets and whatever else, including a gun, which could cost you your concealed carry advantage.
Third: if approached, having your back against a wall is better than not; being in a door frame is better than a wall; and finding an open door, stepping through and closing it is best.
Situational awareness/code orange.