While most police will say that dense landscaping is an invitation to trouble and that statistically houses that cannot be seen from the street are at a higher risk for break-ins than houses that are, there are other landscaping tips they do not stress that they really should. Like their own "3-7" rule, especially if combined with thorny plants. IE: security landscaping.
The 3-7 Rule is to keep shrubs near the house no more than 3 feet high to deprive a potential intruder of a hiding place; Keep tree limbs at least 7 feet away from the side of the house and at least 12 feet off the ground, to deprive the intruder of easy access to a second level window or balcony.
I never knew this rule and am amazed at what good advice this is. Head on over and read the entire post here.