we use a velcro harness and are very happy. he has never gotton lose even when the velcro starts to wear out. i have one from tiger's mom (above post). she does very good work and the velcro is strong. i also have a puppia harness which is very similiar, but had a clip thingy that holds it instead of velcro.
http://www.ipetconnection.com/Puppia_Harness_p/sh01.htm