Can a structure with a barrel tile roof system be sealed to prevent penetration by rats?

Many tile roof systems are constructed of inferior grade, poorly fitting tiles. The openings at the ends of the tiles, along the roof edges, and along the drainage valleys typically are left open. The result is that it is not uncommon for there to be multiple holes and crevices that permit rats to make their way beneath the tiles and onto the roof decking. Imperfections in the decking installation or openings made for Plumbing vents generally provide the means for rats to make their way into the structure. Because tile roof systems typically have multiple openings across the roof surface and each such opening must be sealed to prevent rats from reaching the roof decking, the task of sealing the roof against penetration by rats requires painstaking attention to detail. A mortar seal must be accomplished at the end of each row of tiles and at the drainage valleys. Smaller cracks or crevices appearing between individual tiles must be sealed with an adhesive sealant.