I'm thinking of getting one of these for use on my FF Canon. But I'm concerned about not being able to protect the front element - there is a lot of grease and salt in the air here in Belize that deposits on any glass surface. On my other lenses I have to clean the filters at least every few hours of exposure to the elements. Is it possible to attach any sort of protective filter to the front of this lens? What are the drawbacks of having such a filter on?