Alison, AliceI have St. Patrick's Breastplate as Hymn 370 in the 1982 Episcopal Hymnal. The part you recited above(Christ before me, etc.) is sandwiched between the "I bind unto myself today" verses to a different tune and key. Makes for a great piece. I assume you have this so I'm not transcribing full lyrics. Let me know if you want them.
I actually use the breastplate as personal ritual and found it quite effective as a ward.
I love the lyrics which began this thread, thank you Alice and I will add them to my list of faith stuff. I like the Slane tune with them as well.
Here's to ya. Marc