The mandatory in this case is a cement tube(6.5' wide). Anyway I say if you miss it you have to come back around on the side you missed on. My friend says you should be able to come back though the tube(as long as you make all the way thru) and then go back thru in the right direction. I know the rule book talks about drop zones and penalty strokes but doesn't really cover casual play. I've never really dealt with mandatories before so I'm not really sure what the etiquette is in casual play.