A dremel is going to take an awful long time to get through 3/4" hardened steel. Harbor Freight sells angle grinders for $19.99, sometimes less depending on sale dates. I've used one, in combination with a power inverter and a 50' extension cord from our van to cut off locks for a friend who broke his keys in the lock being an idiot. Its still a longer process than cutting a cable lock, and will likely draw some attention (though I've never been questioned by anything more than a curious eye when doing this) so be prepared to explain what's going on.