Sontag reached the semi-finals of the 1978 British Open, losing to the eventual winner Eric Bristow.
He reached the semi-finals of the 1978 Winmau World Masters, defeating Doug McCarthy and Charlie Ellix before losing to Tony Brown.
Sontag played in the 1979 BDO World Darts Championship, losing in the first round to Ronnie Davies of Wales.
He returned to Jollees for a third time for the 1981 BDO World Darts Championship, losing in the first round to American Nicky Virachkul.
Sontag won the 1988 Witch City Open champion defeating American Andy Green.