And make sure you're not using real weapons..
If it is indeed a fake machete, and not just a machete that you've blunted, then there should be no issues.
I'm from the uber-real school of film making. Get the clumsiest actor money can buy and go with the real machete, properly sharp at full speed, preferably howling kiaaaaaaa at the time and with the neighbours watching. There are a whole host of reasons and just a few off the top of my head:
1. It saves money. No messing around with buying fake blood and a significantly lower special effects budget. It's all real dude!
2. It saves money. One less actor to pay.
3. Publicity. You will have the press camped outside your jail cell begging for interviews, you will be all over the news... members of the public coming around to witness where it happened... you just can't pay for that kind of publicity. Hell, th@t dude from the Actors Studio will be calling you to sit in front of aspiring film students to ask you how you managed to get actors to 'that place.' Remember - no publicity is bad publicity!
4. Realism. It will look good, the screams will sound good and the onlookers' faces will be a picture. Spielberg couldn't get that kind of realism.
5. More realism and money saving. If you wait long enough you will have a whole host of police arriving with real guns, cars, ambulances, the whole nine yards. Guerilla dude - shoot them while they're there! You could even incorporate a chase scene... drop the machete, run like crazy and set up a few cameras en-route. Note that if they shoot you / the actor wielding the machete, this is a bonus! More publicity, another less actor to pay... it's all good!
6. Speed. You can get the whole thing done in one take.
The subsequent courtroom drama will be a movie in its own right and you can bag the rights early! It'll be the follow-up sequel every blockbuster needs!
So there is every reason to chuck, erm, carefully place a really heavy, uber-sharp machete into the hands of the clumsiest actor you can find and tell them to get stuck in. Just go in like a threshing machine on speed. Remember to tell them it's a fake plastic one and the police etc... aren't real - they're just part of the shoot. Guerilla! It's the best way. It's the only way...