I recommend booby traps. Vlad the Impaler had an excellent method of detering unwanted vistitors by putting heads on spears outside his crib. As for traps, a pit trap is classic but no one likes digging. Explosives are entertaining but messy and can cause collateral damage. Falling blades are nice but depends on your location and set up. An electric welcome mat is entirely pointless because of rubber soles. However old concert pyrotechnics are extremely efficient at causing minor damage and a huge scare effect.
