Sometimes, if they can't get to it they'll go and do something else. Not always, but sometimes. There are a good number of sims for whom sprinklers are a manic obsession. But when I block it, I typically hear them freaking out over not being able to go there and I can intervene in this psychotic compulsion.
I find it ironic that they have spent thousands of simoleans of their hard earned money on wall mounted TV's, video game consoles, computers and pools, but despite this, they won't leave the sprinklers alone.