trellis wire

Hi there, My name is Domenick, 25 years of age and living in the southwest of the Netherlands in a coastal area. I have a question regarding the trellis line heights. I want to have some ranks (some guyot and some cordon) but I an not sure to which hight I shall let the stems grow before...

I just got through setting some 6" posts for a 60' single-wire trellis for three muscadine vines...two Isons and one Noble. I plan on running the wire across the tops of the posts. What I've curious about is how best to protect the end of the posts from water sitting on them and promoting rot...