In high school we laways found that braking like a dog (and maybe having one person making seagull mating calls) while charging at the intruders was sufficient to keep them away for weeks at a time.

Also sufficient to get a counselor called in to talk to you.
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Why is it that if someone tells you that there are 1 billion stars in the universe you will believe them,
but if they tell you a wall has wet paint you will have to touch it to be sure?