What you are looking for is Device Administration
http://developer.android.com/guide/topics/admin/device-admin.html
This page explains how it works and how you can change all sort of policies about passwords and disable camera.. et cetera
What they barely talk about is as soon as an application is enabled as device administrator you can't kill it or uninstall it without disabling this feature first. It's up to you to implement enable/disable buttons the proper way.
To be sure the service always restart even if killed by system (in low ressources cases) you need to override this method of your Service :
public int onStartCommand (Intent intent, int flags, int startId)
{
return START_STICKY;
}
Finally to make your service start at boot you need to catch ACTION_BOOT_COMPLETED broadcast.
The main issue is you can't prevent user from disabling GPS or using mock locations but you can detect it and log it.
It is a good practice (actually it is mandatory in my country) to notice users they are watched so you can explain them at the same time that you'll know if they mess up with the GPS.
Rooting the phone is another solution but you will likely open more doors than you close ;)