This is an issue almost inherent in farm strips.
My last strip was very popular with dog and other walkers. Yes they are a bloody nuisance but a conversation with them will usually much help. What will not help is 'buzzing' them.
Remember they have usually got no idea that you want to land - it simply does not register in their empty little heads that the neatly mown section of a field has not been prepared especially for them to walk their dog!
So if you want to cause difficulties for the strip owner/operator and yourself then just try and scare them off.
I'll admit to a few nasty comments to the elderly couple who took to parking their Range Rover in the middle of the strip but walkers - leave them be - 500 odd metres doesn take that long to walk (although it is a real pi**er when they walk to the end and then turn around and walk back!!