Looking into Eire. Pavement change in dip is full of rain water. Notice the sign in the distance welcoming to the county, but there is no indication at all of an international boundary. Second picture is a small stream with old stone bridge. The stream is the border.
The border at the Drumally quasi-exclave. Pavement changes are notable, although not directly on the line. The small square plates in pavement mark the borderline. This is at point L37c on the map below.
The photo on left is at L37b on the map below. The right photo is from L36 on the map below.
This is also L36 looking southwest along the border.
Drumally enclave.
These are shots from a border bridge near Carrickmacross.

 
The same bridge looking into the UK (Carrickmacross), but notice the Eire flag flying on the UK side of the bridge. Clearly a nationalist community on that side of the border.
Left--bridge in a new  residential subdivision near (west of) Londonderry. The small stream in the housing development is the border. A change in pavement is slightly visible, but no other signs of an international border. This picture is from UK looking into Eire. Right--same housing development but other side of the street looking in the same direction. The sidewalks, house styles, and roads were different on opposite sides of the new subdivision.
Left--This is the bridge (change of pavement) above on the left.

Right--This is a bridge over the same stream but about 350-400 meters to the west of the new housing development. Note the pavement change but no signs of entering Eire--looking south.
Left--the UK-Eire border looking northeast on the main highway west of Londonderry, UK on right, Eire on left. The sidewalk ends, but the fence probably marks the border more precisely because of property lines. Right--opposite side of the street. There's a VERY small ditch/stream on the border here. I think the pavement changed just to the left of this photo where the curbing ends. Just think, only a few years ago these borders would have been closed with barbed wire, barrels of concrete, rubber tires, etc!