Chains and metal cuffs. Not police cuffs but the wide steel cuffs with padlocks. Two to three inches wide with a collar to match. Plain steel cuffs and chains have a wonderful industrial feel and there are some custom shops producing excellent quality gear at reasonable prices. The stainless steel stuff coming out of China is beautiful, smooth and also reasonably priced. Once the lock clicks, you're chained until you find the key. Knives, scissors, sharp rocks, dexterous fingers - nothing will get you out except the key. Love it.