Incentives?

I wanted to do an incentive this year for the kids who were bringing their library books back each week.  I found these cool looking library cards, and copied them onto different colors. A different color for each grade level.  I made one for each class. Each teacher has agreed to put their students names on each one for me.  I'll keep the cards in the library for them.  Sooooooo, what do I do with them?  Ill hand the kids their cards before they find their books. When they find the books they want, they will write the names of the books on the lines.  I'll collect them at check out ( the cards).  The next class time, as they check their books into me, I'll have the teacher hole punch beside the books that are brought back to me.  If they get seven out of the nine punches, I will reward them. Wow it's sounds pretty complicated after writing this, but, I am going to give this a try.