I'm calling shenanigans on that. First of all, you shouldn't have to erect a fence, gate or "No Trespassing" sign in order to keep people from violating your property. That reminds me of the guy who steals your lunch from the refrigerator in the break room, and when confronted says, "Well it didn't have your name on it." It shouldn't have to -- you don't need to know who's it is, you just need to know it's not yours. Private property should be assumed to be off-limits unless you specifically know otherwise.
And second, even if your car is parked in a public place, the police still shouldn't be able to attach a tracking device to it without a court order.
I agree, if its not yours you should know well enough not to use it or take it. The only case I think would be the exception would be if it wasnt private in the first place, or you were allowed on the land and the ownership changed all without your knowledge and then you werent allowed on (first offence would be excusable in my mind).
But yeah, without a warrant I believe the police force to be no different than anyone else. If I went and put a tracking device on someone's car right now I would get charged with a multitude of things more than likely (invasion of privacy, etc etc). But if I presumed him to be doing drug deals that makes it ok?
What I dont understand is... if they had all that time to monitor the car wouldnt it of only taken a day to get a warrant from a judge to do this? I know I sure would, considering my job would be on the line.