GPS Logger or Real Time

As a vendor for both GPS Loggers and Real Time Tracking systems, we tend to see a variety of applications that meet the customer's requirement. Most PI companies tend to request the REAL TIME units to assist them on those very surveillance concious files or to track items that have been growing legs. Granted, from time to time, they do have clients that only require the "AFTER THE FACT" data and the logger is used. Which ever one they choose, or should I say- "Their client chooses", it is always in their (The PI Companies) best interest to varify and get it in writting that there is a legal right to place the GPS unit. Some PI's, and other customers too, have stated - No problem- I will just deny puting it there; or- I never install the unit, I get someone else to do it.
Being in the profession for 29 years, I feel that we have read enough jurisdiction and privacy law sections to say- Don't think for a moment that the above statements will get you off the hook if the GPS unit is found. In many areas, you can still be held accountable to some degree if it is not legally placed.
How do you verify LEGAL PLACEMENT?
The simple rule of thumb that we have always used is- Who's name is on the registration of the vehicle? If your client is not on the Registration, they most likely do not have a legal right. This criteria should be used for both Real Time GPS and gps loggers.

Your thought?.. Comments?.. Suggestions?