In this case you must select groups. Belt, rings and part covering pubic between thighs (sorry - I do not know the name) should be selected as constrained group. Moreover you must select as constrained group 1 line of verticles on the top of red/brown cloth which covering front (I do not know this name also). Anyway it is still possible that belt's rings will be deformed and do not fit to the rest.

You can have even better effect if you treat this cloth as hybrid. Select mentioned parts (belt rings etc) as choreographed and bottom of loincloth as default dynamic (except one line of verticles on the top, which should be choreographed)