You need: two sheets of plywood, cut to the dimensions of your door. one sheet of 1/4" steel plate, the dimensions of your door. A bunch of carriage bolts, nuts, etc.
Stack the wood on either side of the steel plate, with lots of construction epoxy. drill a bunch of holes through the stack. install bolts through the holes, round side out, nuts on the inside. Hang door, install locks, etc.
Use a scrap of steel plate bolted behind the striker. Enjoy.
Most doors suck. A solid wood door is tougher than a hollow core, but usually you can still easily bust the lock out of the door or break the door jamb. Lots of heavy steel is about the only fix. (And, if you ever have a run-in with the police, that steel plate hidden in the plywood will give a nice surprise to the pig with the shotgun and some breaching rounds)
Keep in mind that busting in the front door is only one way of getting in - windows, etc are all just as likely.
--Bushytails
