Following a recommendation on TOTV I called out
Devon's Irrigation -
devonirrigation@gmail.co - 352-551-3478
and he was here within three days and did an excellent job fixing the problem
The leak turned out to be under a tree and involved splicing a detour into the main zone pipe rather than just sealing the leak, so his time here was much more than we expected. However, he did ask me after an hour if I wanted him to carry on, and he ended up charging me a very reasonable fee.
Highly recommended.