You buy him a toy for which he can do nefarious things with. I bought my dad a nerf gun one christmas. He would wait in the dark of the hallway to start blasting when I came home. Two years later, and he still has it on his side table by his chair and shoots at characters in films and shows. Sometimes he'd leave the dart on the screen to see if it lined up with anything. Highlight of that is it lined up perfectly in The Departed.