HI Alasdair,
You can usually control the vertical ordering of objects with the outside staff priority setting, Half the fun is working out what sort of object each thing is. A mark is a RehearsalMark. Also, the NR section on Vertical Collision Avoidance is helpful.
== snip
\score {
\new Staff {
\tempo "Faster than possible"
\partial 4
r4
\once \override Score.RehearsalMark.outside-staff-priority = ##f
\mark \markup {\small \musicglyph #"scripts.segno" } |
r1
}
\layout { }
\header{
piece = "A piece"
}
== snip
Andrew