Hi Antique
I’m afraid it’s the price you have to pay for it being a popular place! Only one hog may not mess in the feeding station at all – as you found out over winter. I found the same here. The ones who have overwintered here (and for that time were only hogs) never messed in the feeding station.
I don’t think it’s territory marking, but it may be contributed to by ‘nervousness’ of other hogs being around.
But yes, I think your best bet is to have a washable surface so that if possible you can partially sweep/scrape it up and if you’re lucky enough to have a jet washer, finish the clean up with that.
