HI,
I have dogs, it's the bitches pee which scorches the grass, the best way to deal with it is to water the patch where they have been, as for the doggy poo smell, it does linger of a little while, but it shouldn't last for long, maybe that are strays in the area which are using the garden too or it could be cats, their 's smell worse than dogs, eventhough they scrap earth over it. If you go to a big supermarket or pet store that are detergents that you can put in a watering can and water the patches where the poo has been, which lifts the smell and doesn't harm the grass or any other animals.
Good luck