Hugh,
I think the townland (address) is probably Ballyharigan which I mentioned before. It’s a townland immediately adjoining Drum. This looks to be your couple in Drum in the 1901 census, and I can see they had at least 4 children born there, 1902 - 1908:
http://www.census.nationalarchives.ie/pages/1901/Londonderry/Drum/Drum/1523853/
So if they lived there from 1901 to 1908 then they couldn’t be far away when they married.
The farm that John & Ann were working on in 1901 was plot 15 in Drum which, according to the Valuation Revision records, was farmed by Robert Joseph McKay (McCay in the censuses). That farm today looks to have been consolidated into a much bigger farm off the modern Drum Rd. Plot 15 actually borders Ballyharrigan so they could still have worked in Drum if living briefly in Ballyharrigan. Though clearly they were back in Drum soon after their marriage, as their first child Margaret was born there on 2nd June 1902.
Your family had left by the time of the 1911 census:
http://www.census.nationalarchives.ie/pages/1911/Londonderry/Drum/Drum/…