Drawing the external boundary
The most common external problem is not litter, it is that nobody knows where the responsibility stops. A forecourt runs into a shared carpark which runs into a footpath which belongs to the council. Each party assumes the next one covers the edge, and a strip two metres wide accumulates rubbish for months while everybody is technically doing what they agreed. Everybody is technically doing what they agreed and the strip stays dirty.
Naming the boundary at the walkthrough resolves it. To the kerb line, to the first row of parking bays, to the property boundary at the eastern fence. Those are specific places that a cleaner can identify at night. A description such as the immediate external area is not, and it will be interpreted differently by every person who works the site. A place a cleaner can point at is a boundary; anything else is an interpretation.
