Help Anti theft app please help


Hello every one.. my teen ager son has Sony experia z3 . And i would like to put a monitoring app in his telefon. I have already tried many but most of them has a mailware since he has Avast antivirus. So i got an idea to use anti theft app. Can some one Recomend an app for me please ? But it should be :
1- 100% un detectable
2- he Cannot remove it unless i do it because i have the Admin rights.
3 - no mailware so the Avast can detect.