Pls help not sure what I am doing... tilt sensors

I am thinking of using tilt sensors as a way to keep anyone off of my roof. Believe it or not I have gang members who climb onto my roof to compromise my security system.
Since my roof area when a person walks up there deflects as its wood I was assuming tilt sensors would be appropriate. The only thing is I live about 200 feet from a railroad line which produces vibration that I dont want to have false triggering the system since I will have an audible alarm connected to this. Can anyone suggest if there is something better I can use or if my approach is right then which modules should I use.
From the aaduino I will then use a relay to activate the siren.
Once I can get started I will worry about the sketch as Im new and still havent learned how to master writing the code.
Thanks so much for your help…
By the way PIR motion sensors that I use in the past were merely disabled by them, I do have a microwave sensor module that works on the 1.2 gig band Maybe this would be best? It has three wires one for output of course to hook up to the dig pin of the auduino can this work?

Barbed wire has worked for me. I think you are right about vibrations from the RR. If the intruders are sneaky at all, they will be able to vibrate less than a passing train.

Consider using a passive ir motion detector:

I would have thought that you could write software that would distinguish between the rumble of a train and someone walking based on how often the vibrations occur. Or maybe have a second vibration sensor inside that can pick up the train but not vibrations from the roof.

However- if you detect that someone is already on your roof what are you going to do about it? I doubt that they are going to be deterred by a siren if they have made that decision...

I second the wire suggestion. Black trip wires would be as effective as barbed wire.