Could you build a fence maybe (ie, sort of a canopy without a top) - stays with the open-top concept, but might help encourage keeping escape artists on the inside? 
		
	
		
		
		
		
			
				__________________ 
				 -- Tony 
 My next hobby will be flooding my basement while repeatedly banging my head against a brick wall and tearing up $100 bills.  Whee! 
 
			 
		
		
		
		
	
		
		
	
	
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