Posting signs that the soil contains hazardous chemicals also works for  some 
bottle hunters, but then that implies the cretins have to be able to  read.
 
Out here in the Far West, signs that alert diggers that the soil is  
contaminated with Valley Fever have also worked in the past. Not to mention a  sign I 
once saw in Sacramento that the privy soil contains Chinese liver flukes  that 
can enter the blood system from small cuts to the hands.
 
Ron May
Legacy 106, Inc.