I think the biggest deterrent is an old boat and conservative lifestyle. Difficult as it may be to do, just look like you've got nothing they want. Stay away from areas known to be problem spots. Any more aggressive approach will just get you more trouble than you want. Remember, petty crime is just that. Let them have whatever it is the want.
There is a tide in the affairs of men,
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
Shakespeare, Julius Caesar IV, iii, 217