Getting my father to clean?

He's driven my mother crazy for a long time, and me as well. He's always got piles every where.
I have decided to join them on their "Marriage counceling" and bring up the issue.
I'm worried it will bring problems between my father and my self, but he REALLY NEEDS HELP! And won't talk to us about it.
He gets crazy mad when we try to talk to him about cleaning up his mess which is ALL over the house!
He has an "office" that is SOO piled high with stuff and there is NO floor, he never goes in there, and to top it off it's the same place we have our wash and dry, so we can't do any washing in there!
Then he started to put piles in the guest room, so we offered to have him move up there permenantly but he won't do it. OR clean the office.
SO I'm worried my presents at their marriage meeting will upset him!
ALSO I'm worried that he won't change, if anyone could give me some advice on how to talk about it I would apreciate!
I've never been to a theripest.

It is time for him to learn a lesson! Treat him like a child. Let him know that if he doesn't start to clean up his mess that there will be consequences. Let him know that if you and your mother have to clean up then anything that is not put away will be thrown away. HE WILL GET MAD! But you need to explain that if these things were too important to throw away then he should take better care of them and therefor put them away. He is a grown man and should be ashamed that he has to be treated like that, but it will work. How do I know, do you ask? Well after my back surgeries I became very used to my wife and kids picking up after me. Even after I got better and was able to do things on my own I seem to become lazy and would let thing just sit around and expect them to still do it. Then My wife took drastic measures and gave me the ultimatum, either I start cleaning up or things of mine would be tossed out. Well I thought she was kidding until a lot of my things went missing (From tools to clothing). It took only a week for me to get the hint and since then I now clean the entire house. Do the laundry and let her relax on the weekends. Now your dad may not become as I did but it may make him atleast pick up after himself.

You know, it could be that your father has problems with wanting piles of stuff around. He can't throw anything away, and thinks he needs all this stuff for sometime in the future. Have you tried slowly to toss some stuff when he wasn't there? It might make him mad. Anyway, a therapist is someone you can talk to regarding certain things that bother you. He or she will explain to you what you can do to alleviate the problem, or show you another way to deal with things.