Best way to sanitise/dispose of soil with cat poo?

Kia ora, What is the best way to deal with soil that cats have used as a litter box? Is there a way to kill toxoplasmosis after removing the poo or is it better to just remove all the contaminated soil and replace it with fresh compost?

Secondly, after dealing with the garden, what is the most effective way to deter our cats from pooing there? I saw that Wet & Forget have a motion activated sprinkler designed for this purpose - has anyone tried these and how well do they work?

Thanks in advance.