You have to first catch the culprits and, secondly corroborate the offence before proceedings can be undertaken.
The answer lies in technology.
First, small CCTV cameras could be hidden in lay-bys in known "fly-tipping" sites. You see their use regularly on TV wildlife programmes.The camera could detect vehicle number plates, allowing criminal charges. More importantly, this would need national support from the Scottish Government, which would coordinate the operation.
My main idea is the use of electric tricycles with a large collection box on the back clearly marked "Litter/Dog Warden". Such vehicles are in use in the Far East.