I have a slightly different take on the sacrament prayer and the baptismal requirements than what I have seen in most wards and branches I have attended. In each case, I accept fully the idea that the words have been given by revelation and should be repeated verbatim (and that a baptism must include full and simultaneous immersion to keep the symbolism intact), but I believe the administrative form is almost completely adaptable. I believe we should do anything within reason to ensure that the ordinance need be done only once (or only one additional time when a mistake is made) - and can be done by each and every worthy Priesthood holder.
If that means one Priest places a hand on the shoulder of the kneeling Priest and squeezes the shoulder of the one saying the prayer if a mistake is made (so that the one voicing the prayer can correct immediately and not need to repeat the entire prayer) - or multiple brethren stand in the baptismal font to help immerse an unusually heavy person - or someone “coaches” an illiterate Priesthood holder (or one who simply cannot memorize the prayers for some reason) one small phrase at a time - or the person being baptized sits on the floor of the font while someone holds down her legs to keep her feet from coming out of the water - or a mute Priest signs the prayer with hands above his head while the members in the congregation (all having been taught the prayers in sign language) keep their eyes open and watch the prayer being "said" (or another Priesthood holder verbalizes the prayer as the mute Priest signs) - or someone signs the prayer for a deaf member in the congregation - or any other method of ensuring that every worthy Priesthood holder feels confident that he could administer the ordinances as designed, then so be it.
If, for whatever reason, the baptismal ordinance needs to be repeated, I believe the presiding Priesthood authority should explain the need to the observers PRIOR to the repeated performance - and take whatever additional steps are necessary to ensure that one more time will be enough, again explaining what is being done and why. (In my opinion, a third attempt is a failure of leadership.) I also believe any time the sacrament prayer is repeated, the person conducting should explain immediately following the completion of the administration of the ordinance. In each and every case I have observed that the explanation has been presented properly, the Spirit was stronger than it had been initially.