a long glass vase can work really well for this. A buddy had gorilla crab hitchhikers and we used one to trap them. 
 
put some raw shrimp at the bottom, leaned it at a 60 degree angle against the rock, and turned out the lights. by morning we had 2 out of 3 crabs caught 
		
	
		
		
		
		
			
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				There's only two people in the world that I trust. 
One of 'em's me,...the other's not you.
			 
		
		
		
		
	
		
		
	
	
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