You should either use switches or death counts. When the zergling goes in the location set switch 1, when switch 1 is set start the bounding stuff and when it croses and hits the location after it clear switch 1. Or death counters set death for X when you bring it. When the death of X is 1 start the bound and when you cross it set the death to another number other than 1.
Death Counters
http://www.staredit.net/index.php?tutorial=124Switches
http://www.staredit.net/index.php?tutorial=116[right][snapback]357502[/snapback][/right]
solved.
It almost seems like the ling has to be on the location for th bound to keep going. Switches would be the best way to do this.