Horse and trailer issues?

My horse hates trailers. Everytime I try to lead him in, he plants his feet and won't move an inch. Can someone help please?!?!
Update: WOW!! all of you gave me great advice!! i'm going to try several of the methods that you all told me. Thanks everyone!! i can't give a best answer for this one, so i'm just going to have to put it to vote.
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