Thanks for all your replies. Dont think I will be throwing any water on my dog though!!

I dont have a large garden and there really is no other option than for her to go on the grass.

She will often go out unsupervised so I dont always know where she has gone.

I suppose I was looking for something that I could maybe put on the grass as either a treatment after the event or something that I could treat the grass with that would stop the discolouring in the first place.

I have heard about something that you can put in a dogs water that helps with this problem but I would rather treat the grass than the dog.

Mark