Strange behavior, please help.

Ok, I recently came into possession of a two year old male chocolate lab. He is very well potty trained, he comes very well to his name, he sits on first command, yadda yadda yadda. When I first got him, he was absolutely terrified to go down the basement stairs. I'm not sure if it was a natural fear or a conditioned fear, but since we wanted to put his food and water in the basement, I decided to ease him into the basement. After about a couple weeks of coaxing and treat giving, I got him down about half way before he would grab the treat from me and scramble back up as fast as he could. Because of his behavior it seemed to me he was conditioned to not go in his previous owners basement, so I figured once he knew it was okay to go in ours, he wouldn't have an issue. I had my dad help, and he picked him up and carried him down while i held my hands over his eyes and soothed him as we descended. Once he was down there he had absolutely no trouble, and from that moment on he ran up and down the stairs with ease on a daily basis. About a week after we got him accustomed to the basement, was the first time he was left alone, and he was left alone for about two hours. Before leaving I let him out and made sure he went to the bathroom, and departed thinking he would be fine. When me and my family returned, my trash had been torn apart, and he had peed and pooped all over the basement. My first thought obviously went to separation anxiety, when we left he didn't make it a secret that he was unhappy about it as he tried to dart out the door between me and members of my family. I cleaned up the mess, sprayed lots of Lysol, as I've heard that you have to get rid of the smell because dogs will mark their scent and then go repeatedly in the same place. I looked up tips on separation anxiety and planned on starting easing him out of it as soon as possible. This incident was two days ago, and since then I have not left the house, and I have not even been home alone. I went into the basement today to find a huge puddle of pee in the exact same spot he had peed before. Because he did it with people home, even though he is very well potty trained and didn't go once on the main floor since the day we got him almost a month ago, I thought maybe for some reason he thinks its okay to go in the basement, and thats why his previous owners trained him not to go there. In addition just to give some more information, I let him out regularly whenever he gives me any sign that he may need to go, and I walk him for at least 45 minutes every day, and I really don't think in either incident that he did it because he couldn't hold it, but for another reason.

SO, my question is, do you think he has separation anxiety, and only went to the bathroom in the same spot again because I was unable to get rid of the scent? OR do you think that for some reason he thinks its ok to go to the bathroom in our basement? Any tips to train him out of this behavior before it becomes a real habit would be much appreciated.

Do you know the previous owners? His fear of the basement may have been well founded- whoever owned him last could have been forcing him to stay in the basement. And if they were so ignorant as to do that, I am sure they were not potty training him properly and maybe letting him dirty in the basement as well. He should not be permitted near where he dirties at.

I also wanted to mention that he should only be allowed in the basement to eat and drink. I was told this- if your pet has constant access to food and water, they will have to constantly go the bathroom! Feed him in the basement if you wish, but make him come after he is done eating and go straight outside. I wouldn't let him eat again until its his scheduled time to do same.