I can’t see the marriage in the civil records. The 1911 census says the couple had been married 15 years so around 1895/96. Sometimes priests omitted to copy a religious marriage to the civil authorities. So it’s possible there’s a record in the church but not in the civil set. Big Dog is in the RC parish of Devenish. Their records for the 1890s are not on-line anywhere so far as I am aware but you could contact the parochial office to see if they have the marriage in the original register.
Not certain but I think the nearest church is probably Derrygonnelly. (If I am wrong they’ll surely know the correct one).
Fr. Cathal Deery, PP
Parochial House,
Derrygonnelly,
Co. Fermanagh. BT93 6HW.
T: (028) 6864 1207
E: office@bothaparish.com or fr.cathal@bothaparish.com
Sorry can’t suggest what Denis may have been caretaker of.