tenant hanging too many pictures/items on wall

[Kevin McDonald]

I just remodeled one of my rentals (tore down to the studs everything new).  My new tenant has moved in and has  been in the house for about 6 months.  I have noticed the few times I have been called to the house to take care of things they have the walls covered with crap (pictures, little shelves with items on them, etc....).  The house was freshly painted (wall all painted in different colors, etc....).  I feel that when they leave I will have no choice but to repaint the entire house.    How can I write my lease to protect me from this?  They have been great tenants and if they end up being at the property for 3/4 years I really don't mind repainting the house.  I just feel if they leave in a year I will have to repaint, can I deduct this from security deposit?  

suggestions? 

Thanks