lab - chewing and scooting

Question
He's 3 years old... Is this chewing typical?  And I feel badly crating him for 8.5 hours... Any other ideas?
And he isn't licking his behind.  Is it common to see an unclean anus with anal gland problems?
Thank you!

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Followup To
Question -
Hi!
I have two problems.  First, my dog's anus has been dirty over the last few weeks.  His stools are fairly firm, so I'm not sure why this is happening.  He's been dragging his rear on the carpet, blankets, etc., and it is leaving a very unsightly mess.  Any suggestions?  I haven't consulted a vet yet.
Second, my lab is crate trained, but I usually have the door off the kennel so that he can come and go as he pleases.  I shut him into my room to ensure some containment (he will get very destructive if left alone in the entire house).  The problem is that he randomly chews things.  He never chews when I am home - only when I leave.  For weeks he will be fine and then for some reason, which I have yet to determine, he'll go on a chew fest.  Today I came home to find that he had chewed up a cd and cd cover.... Sometimes he will get my brush, or other items with my scent.  The pattern is not consistent enough to be separation anxiety, and I leave him with a bone...so not sure what to do.  Help?
Thanks!
Answer -
The dragging the rear is usually anal gland problems.  a vet, or even some  groomers can empty them.  You might even ask them to show you how.  

The only good answer to the chewing is to shut him in the crate.  Maybe in another year or 2 you will be able to leave him loose.  

Answer
The dirty anus is not common.  Maybe have him checked for worms.  He is eating mostly a comercial dog chow?  

I hate to see a dog crated that long too.  Can you find somebody to give him a mid day break?  A neighbor, or even a professional dog walker?  Many Labs start to reduce the chewing they do after 3 years old.