Turnovers!!

Emphasize "ball security" through sound technique and solid execution.

First you need to assess WHY fumbles are happening.

Don't put TOO MUCH attention on a fumble (during practice) - just correct the error.
Was it poor technique?
Was it poor execution?

If it's only happening in full contact (games) - watch the video and then make a plan.

We dont allow our backs to carry the ball in one arm, until they clear the secondary. They use a 4 point cradle, until they are out in the open. We also use the high tuck carry (ala Tiki Barber) when they do. You have to punish fumbles in practice very strictly. We also teach them that if they do drop the ball, and they will, if they cant recover it , to swat it out of bounds.

Any back who puts the ball on the ground- whether in a game or practice- has six "tunnels". We have a power tunnel, one of the old type with tires and getting through it is tough. Through and back is one "tunnel". Six trips gets their attention. So does some bench time which could also happen.

Let's talk a little about technique when carrying the ball. I'm a fan of the high-tuck cradle as you call it, with the carrier's finger(s) over the point and the ball snugly fit into the crook of the arm. You have to coach them up on how to run and be comfortable with the ball always like this. I also like it when they put it in the cradle and then put their other hand on top of the ball lightly for protection.

But I do not like (a) the four-point carry through the line, or (b) switching the arm that the ball is in mid-run. Now, I understand the theory behind both, that the four-point with both arms ought to be more secure and you watch to switch the ball away from defenders, but I think the four-point ends up creating more spots and less leverage so that the ball can be ripped out (it's kind of a slippery slope, if you can pull on one arm the ball starts to move and then your four-point or double-nose hold spits the ball out) and the switch makes the ball vulnerable when you're doing the switching.

Any thoughts?

Note: The biggest problem with fumbling you see at every level of football is the QB. He must be taught to hold onto the ball with both hands for as long as possible. QBs are horrible ball-handlers and they emulate the poor technique they see on Sundays and Saturdays (ball in one hand while standing in the pocket), which leads directly to fumbles. I call this the Kurt Warner disease. The man has been around for a decade in the NFL and has lost several jobs because he is incapable of learning to hold the ball with both hands in the pocket.