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Please Help

I have three cats that I love dearly.  They are all house cats and I try to keep them stimulated.  All three are males and two out of the three of them have been fixed.  The last one will be done soon.  They are extremely clean cats, I have three boxes for them to use.  Two of them are located in the cellar and I have one on the second floor of our home just in case they cannot get in the cellar.  My problem is they are scratching my walls.  They have made a mess out of the walls on the second floor of my home.  My husband has fixed them just today, but he will not keep doing it.  He loves them too, but he does get frustrated with them.  I have scratching post hanging on a few of the doors in our home, which two of them have taken to.  But I still have one who is just not going to do what I want him to do.  He is my oldest cat, he will be three in February.  That is not the only problem I have with him either.  When our oldest son is home from college, Archie does a lot of hissing and trying to scratch him.   He used to do that to our youngest as well, but I think he realizes that Cory is not leaving.  Any suggestions would be appreciated.  I am wondering if clicker training would be helpful.  Please, if anyone has had the problems I am having and they have solved them, please let me know how.

Thank you