Here’s my take on it.
Puppies need to walk, to be able to explore their environment. The best way to do this is tethered to you, rather than in a sling of some sort. Does your company frequently see dogs on the floors? If not, I don’t see why he can’t be on the floor.
Use the crate more than occasionally. If you cannot have him tethered to you, he should be crated. I would also consider picking up an xpen so he has a safe space to play outside of the crate from time to time.
Frankly, I like the idea of taking him in to work right away, especially if you’ll continue doing that when he’s an adult. If you don’t intend to continue taking him in when he’s an adult, I don’t think I’d do what you’re planning, simply because he’ll wonder why you’re suddenly leaving him home when he’s older.
Dogs will soil where the eat, sleep etc if they have been kept in areas where they had no choice from a young age. A dog that is a soiler takes months of work. This is not a problem that is solved in just a few weeks. there are no quick fixes for this. First, you have a coon hound. this is a high energy, hard headed dog, that likes to have a job. A really tired coon hound is usually a good coon hound. Hounds are very hard headed and can be very difficult to train, especially once they develop habits that they see as no problem for them. Keeping your dog in a crate may never be the answer, but keeping him in an outdoor run only when you are gone may be something that works for the dog. They have really nice runs now days that are very comfortable for the dog ie shade etc. also continue to keep him in the house with you whenever you can, and work him. Get him started in something like agility even if he is not good at it. Keep him busy, tired and with a job to do. Keep an eagle eye on him when he is in the house with you and make sure he has regular bathroom breaks. He may never be able to be left in the house alone, but if he is a great dog and you make the changes that you can, he will still be a good companion and pet.
I’m so sorry you’re having a hard time. It is impossible to help you over the Internet. You say you had a trainer – what kind of a trainer and what did they do exactly or what they had you do? You tried working on anxiety – again, what did you do and for how long? You tried crate training – what size/type of crate and how did you introduce it, how did you crate-train and why exactly it was a no go? Punishing, of course, never works. You say it’s one particular spot only? Is it when you leave for any period of time? Did you try a nanny cam to learn what goes on exactly when you’re not home? I would recommend finding a better trainer (not all trainers have been created equal). On the very off chance, there is one thing Dr. Stanley Coren was recommending some time back for a dog who soils on particular spot in the house = redefining the area. What he was recommending was to put the food bowl in that spot, or play in that spot … redefining the area to dining or play area. The reasoning being that a dog won’t soil where they eat, play or sleep. Migh as well try that. But likely need a good, reputable, positive trainer.