There are 2 problems with wet ground. The fact that you are expierencing -- the club starting in a steep angle as it sould with irons and you hit just a little behind it and the club just keeps going down and down and down with nothing to stop it. The second is your feet. They sink, raises the ball up. So you are more prone to hit behind it even more.

The first solution is to know this. And next it to counter it. Choke up as much as you think you are sinking. Be ready to take more club if you choak up more then an inch. You will now be hitting it lower and with less carry, so you really have to think about what you have to do to carry the ball to your landing spot. The only good thing about wet conditions is that the ball will generally stop dead on the green creating a nice deep crater. So you don't have to worry too much about a low running shot going over the green.

The second solution is learn to pick a ball clean with a shallow attack. Moving the ball back is not enough. That creates a steep angle. To get the shallow angle, take a driver/3w mentality over your irons. Take the club back low and long with the shoulders...big shoulder turn. Use as little hand set as you can stand. Think sweep up on the ball. Put your eyes in the front of the ball and try to hit that part first.

All these things will help you in the slop.