In 1581, he campaigned against the clans of Kavanagh and O'Toole, and on 30 August 1581 was commissioned to follow the lord deputy in the government's campaign against Fiach McHugh O'Byrne, a rebel leader whose fastness lay in the Wicklow mountains. During that campaign he was engaged at the Battle of Glenmalure in charge of the rear guard, and covered the retreat of Grey's forces after they had been routed from the glens. At the end of the year his troops were discharged, and he went to England to seek further employment from the queen's principal secretary, Lord Burghley.