The best thing I could suggest is a fence and gate surrounding your property.And a few Pits or Rotts running loose inside of the fence.They most likely wont come in there without you being there..Or gunshots.
As far as I know, lack of any trespassing signs means anyone can come on your property, but not inside your home.
This means if kids are playing and their ball goes into your backyard, they can retrieve it. Cops can come take a stroll through your property as well. Only your HOME and the INSIDE of it are protected UNLESS you explicitly state NO TRESPASSING.
For more details look at USA vs Juan Pineda-Moreno
The decision was not unanimous. In a strongly worded dissent, Chief Judge Alex Kozinski said that because of the ruling, "1984 may have come a bit later than predicted, but it's here at last."
In the 10-page ruling, two of the Ninth Circuit judges held that the DEA agents did not violate Pineda-Moreno's constitutional rights. The judges ruled that because Pineda-Moreno's had not taken specific steps to exclude passersby from his driveway -- by installing a gate or posting no trespassing signs, for instance -- he could not claim reasonable privacy expectations.
The Ninth Circuit panel ruled that the actions by the agents were comparable to the delivery of newspapers to the house, or the retrieval of a ball accidently thrown under the vehicle by a neighbor.