I nice fun dog. It doesn't have to be an attack dog. It helps if it is a smart dog. Or a dog that you're very afraid of, those aren't as much fun, but very effective.
Replace all your crappy door locks with real professional grade door locks. Upgrade your door jams so they can't be kicked in thus negating the effectiveness of your awesome new locks.
Some alarm system stickers for your windows.
A couple fake video cameras.
You've spent maybe a few hundred dollars, and prevented 99% of all criminals from invading your home, and you have a new friend (the dog), or possibly a terrifying dog that you can use to intimidate Jehovah's witnesses.