Hi, I know it is a stupid question but I really really need help.

I bike to school and for the past week some people have been letting the air out of my back tyre and i cannot think anyway to catch them, or stop them.
I was wondering if you guys knew anything i could do to stop them getting my dustcaps off or letting the air out of my tyre.
Please help me as it is upsetting having to walk all the way back to my home.
Thanks