Depending on your army will depend on how to deal with them best... for ex. if you are more shooty but slow you actually might enjoy things like this, or if you are really manuverable you can just go around to one side and focus shots the same way. Normally the best way that I have seen to prevent this from happening is to either have really small squad sizes so that if you get charged that unit will be in the open next turn...

or just to charge them first on a side of the unit. That way you a) get more attacks and b) use the defensive reaction to your benefit by drawing their assault units to the sides of the board and out of the way. Normally they are a good thing, though as you just explained...