What exactly is the concern? Are you in flower and don't want buds getting wet or is it plants in veg and you're worrying about flooded pots? Do you have a covered porch or some sort if awning? There are lots of DIY "hoop house" projects using PVC and painters plastic drop cloths for making greenhouse like structures.
I wouldn't worry about plants in veg unless they're seedlings. If you can't cover flowering plants, shake off the excess from the flowers after the rain stops.