adding a shock sensor to a 2000 camry

Hi, I have a 2000 Toyota Camry with an OEM dealer installed VIP RS3200 Plus security system which includes a glass breakage sensor. Thanks to the neighboorhood kids throwing balls I now have two dents in my roof that is going to cost me $200 to remove. I would like to add a shock sensor so if this happens again maybe I can catch who did it. I was reading the alarm owners manual and the GBS has a warn away feature that will flash the lights and sounds the horn for 20 seconds. If it detects more tapping or breaking of the glass it will flash and honk the horn for 60 seconds.  I see most of the shock sensors have a dual stage feature too can this be intergrated into my system or should it be wired some other way? If it's too complicated for a novice I will take it to an audio shop. I would value everyone's opinion that way I dont get blindsided and to make sure they do the job right. Any help will be greatly appreciated.

Thanks all.

The 20 second horn honk warn away is straight from the RS3200 manual the only thing that can trigger the warn away is the GBS. Any other triggers will cause a full 60 second horn honk. Thanks for the info kenwood_nut do you think a DEI 508D field intrusion sensor would be a better way to go?

I do live on a busy street with lots of motorcycles, cars with loud mufflers and cars blasting their subwoofers. I'm going nuts constantly looking out the window making sure the neigborhood punks are not throwing footballs or basketballs near my car. I have just found another dent this time on top of my hood.

My car does have a piezo chirper when arming and de-arming the car. If you try arming the car with a door open it will sound a constant chirp/beep to let you know a door is open. I was hoping that either a shock or proximity sensor could be wired  in such a way that the warn away feature could be wired to the piezo chirper instead of the horn and the second stage could trigger the horn honk.

Does anyone have more ideas if this will work?

The Toyota RS3200 VIP (Vehicle Intrusion Protection) is an OEM alarm that is port or dealer installed. It is made by Fujitsu Ten for Toyota. http://www.toyotaownersonline.com/pub-share/pdf/security_system.pdf I have the owners manual and this alarm does not have that remote feature. Also I never asked about disarming the GBS.  

In a nutshell I have an OEM alarm that does not have a siren but uses the horn. It has a piezo chirper that chirps. In conjunction the parking lights flash to give confirmation of door lock/unlock. 1 chip/flash=locked      2 chirps/flash=unlocked. It also will make a constant chirp sound if you try to arm the car with any door not fully shut.

I would like to add an aftermarket shock sensor to the factory alarm. I have read on many forums that you won't be able to use the warn away funtion. I would like to know if the warn away could could be wired to the piezo chirper and the second stage honks the horn?