First things first ..... you're getting aggressive behavior because you're acting aggressively to your dog
You never spank or hit a dog unless you want an aggressive response from him

You need to claim the table as your possession
Have him in the room with you ... the minute he jumps up
AH! ... or Clap your hands
You need his undivided attention
and down he goes
GOOD BOY!
You do this for as many times as it takes
Then when you think he's got the idea put something up on the table that you know will grab his attention and start all over again

Things are getting SOME better! The other day we went to a huge park for a couple of hours. It was a fenced in park, so I decided to let him off his leash. He LOVED it, but I started to get scared when I couldn't catch him. I got his attention, and turned around and ran the other way, so he ran to me. He was so tired that he couldn't stay awake on the five minute drive home. He still chewed on things that night after I left him alone. He usually bites my ankles and cries LOUDLY when I try to leave, but that night I said, in a really stern voice, "Maxwell! Sit!! Stay! NO BARKING!" and he, miraculously, stopped. It almost always works when I leave. He still hasn't realized that I'm in charge yet, but I feel that things might be getting better. I give him treats more when he does good things, and I make it a point to give him so much attention it's sickening if I come home and he hasn't destroyed anything. He's just finally acting like a decent dog does... It's still gonna be a while before he is obedient. Thanks everyone, for your help! And I'll keep updating!

That's great! Of all the stuff you described, separation anxiety can be the hardest to fix, so I'm really glad to hear you two are making progress with that.

It sounds like he has free run of your place while you are gone? Have you considered getting him an xpen or crate? That would help with his destruction, given that he can't destroy stuff he can't get to ;), and it's also a huge help with potty training.

Thanks for letting us know how you're doing.

I agree with everything the other post said. To get him to realize that you are the leader, you need to control the resources. For example, do you free feed him? If so, change to scheduled meal times. Before you put down his food, he has to perform a command. (I have taught Cash to sit and stay until I say the release word and only then can he get his food.)
Also, after 15 minutes, take the food away and give it again at the next meal time. I promise you, he will only go hungry once.

Other leadership tips: Always have your head higher than his, claim the best spot on the couch for yourself and always enter a door before he does. This firmly, but subtly lets him know that you are the leader and that he is second-in-command.
As to the separation anxiety, ignore him for 10 to 20 minutes before you leave and after you get home. I know it is difficult, but it works. Leave a radio on so that he doesn't feel alone and give him some intelligence/activity toys, like a treat ball or a kong. Only greet him when he has calmed down - if he goes crazy like mine do.
When you get home and he has done something bad, don't yell at him or show anger. Just put him in a safe place (out of sight) and clean up what he did.
Remember that the leader is calm, confident and assertive. Keep your cool. When he is good, acknowledge those behaviors and when he is bad, simply ignore him.

Good luck. Let us know how it turns out.