Are you sure you have it wired right? It supposed to shutdown after about 30 seconds or something close to that if the sensor does not stop reading high.
Putting that aside if your having some kind of misting issue you could make a DIY dome that covers the sensor from water spray but is open on the bottom and has an air hole at the top. Drilling a hole the same size as the sensor threads into the side of a 20 ml dosing cap and then putting the sensor through the hole and using the plastic nut to hold the two down should work.
Sorry for the crude drawing but I just did this quickly in MS paint to show you what I mean