The CFL has a rule covering those situations, often where the football field is surrounded by a track.
Article 2 — Fields Less Than Regulation Size
If the regulation length of a field is not available because of a fence, a running track or any other object, a clear line of demarcation shall be established at least one foot toward the playing surface from such fence, track or object.
A line shall be painted on the playing surface and shall be considered as the boundary line. A player who touches this line, the surface outside the line or any object outside the line shall be ruled as having gone Out of Bounds.
CFL games played at the Liberty Bowl show why 20-yard endzones never caught on: https://www.reddit.com/r/CFL/comments/10kc6f1/cfl_us_expansion_quirks_memphis_mad_dogs_unique/
The CFL has a rule covering those situations, often where the football field is surrounded by a track.
Article 2 — Fields Less Than Regulation Size
If the regulation length of a field is not available because of a fence, a running track or any other object, a clear line of demarcation shall be established at least one foot toward the playing surface from such fence, track or object.
A line shall be painted on the playing surface and shall be considered as the boundary line. A player who touches this line, the surface outside the line or any object outside the line shall be ruled as having gone Out of Bounds.