OMG, I agree with Mr. Claxton!
A leg-mounted cargo pocket is no place for a concealed weapon.
My reasoning is different, though.
Leg-mounted cargo pockets do not permit quick, smooth access. First, you have to undo a button or snap. Then, you have to bend either your leg or your body, to raise the pocket to hand level. All this takes too much time, and cannot be done quickly or smoothly.
However, carrying a pocket pistol in the upper-front pocket of cargo pants makes a great deal of sense. I do it all of the time.
The cargo pockets are used to carry all of the other stuff that you'd normally carry in that upper-front pocket.
(I carry my reload in my left-leg cargo pocket. I can access it quickly enough, especially from behind cover.)