We are using drupal percentage coupon module. When customer add products admin>store>products customer can select if this product is on sale (if sale there is a discount)

http://i.stack.imgur.com/YWsBN.png

if its a sale and selected some percentage, he can enter the price for product and save item.

Problem is when we have given discounts for these products already and when redeem the coupon again some percentage applies for these Sale items.How can we limit not apply coupons for these sales items only for other items.

Thanks