Basically you can belt them with anything which comes to hand (e.g. an umbrella, a knife, the TV) but nothing that constitutes a pre-planned weapon (e.g. a golf club, lead-lined bat etc). As long as you can explain why you had the implement with you at the time it's ok. (So a knife in the bedroom is out of the question, but in the kitchen it's understandable). You also have to demonstrate your need to use the weapon, as you can't e.g. practice knife throwing on the bloke climbing the back fence to get away lol. You have every right to defend yourself and your property, and as long as you can explain away what you did as reasonable then you'll probably get away with it.