If you wear veneers won't your real teeth underneath get all rotten?

Hello, 
As long as veneers were properly bonded and and are well maintained brushing and flossing, the teeth underneath are isolated from the oral environment. This means nothing will happen to them.

There should be no problem of decay forming under properly bonded veneers. After etching and bonding the veneers they are sealed onto the enamel with no room for decay to take hold

dental veneer is thin layer cemented on front side of tooth. so there is no chances of infection under veneer. but in case of faulty cementation, cavity may occur under veneer. clinically dark black colour appears on veeneer, indicating cavity under veneer.