<human>: Can you summarize the given text in a few sentences?

Hi Doggit,

Two weeks ago, I found this dog in a dog park and took him in, thinking I could find him a home.  [Poor little dog!] I have taken him to the vet and gotten him updated on shots and now I'm looking for a good home.  The vet says he is about 4 years old and healthy.  Unfortunately, he's not neutered.

He seems to be housebroken, but when I leave him alone in the house, I always come home to find he's marked somewhere in the house.  I don't believe it's a bladder control problem.  It may be some separation anxiety.  The first few days I had him, I tried to keep him on my enclosed porch, but he worked his way out.  Since then, I've been letting him have the run of the house while I'm out.  Everything is always fine except for the marking.  How can I stop this behavior when I'm not around to police it?  I'm hoping to get started on it while he's with me so he'll be better for his new owners.  Would neutering stop it?

The only thing I can really think of is doggy day care, but that won't solve the problem for his new owners.  Otherwise, he's very adoptable - super sweet, friendly, happy little guy. I want to improve his chances as much as I can.

Thanks for your help!

Other relevant info:

- I have another dog (male, neutered, awesome, [obligatory] that is allowed anywhere in the house.

- I have read about crate training, but everything says you have to ease the dog into the crate over a long period and I have to work every day.  I don't want to increase his separation anxiety by botching crate training.
<bot>: I have temporary custody of a dog that marks in the house when I leave him alone.  How can I stop this?