GPS tracking devices are all the rage. They have become so portable that you (or a private investigator) could attach one covertly to your spouse's car and record all of the comings and goings of that vehicle. That may seem like a very cost-effective method of surveillance, but if the car is titled to or leased solely in your spouse's name, you could be running afoul of the law. Virginia Code Section 18.2-146 makes it a Class 1 misdemeanor to "individually or in association with one or more others willfully break, injure, TAMPER WITH or remove a part or parts of any vehicle...for any purpose against the will or without the consent of the owner of the vehicle...." This "can" be interpreted to include placement of a GPS tracking device, and you can be responsible criminally even if you hire a third party to do the dirty work.
You need to talk to an experienced Family Law attorney before you undertake any action. There are potential legal consequences to anything that you may do, especially when it involves technology.