If I have to leave him at home I want a larger pen so that he can move around more than in a crate. I had something similar to this but he can get out of it:
Pet Dog Cat Tent Puppy Playpen Exercise Play Pen Crate - eBay (item 260597733410 end time Aug-03-10 11:55:06 PDT)
There are these also. This one is 48" high:
It'z a Breeze Mesh Exercise DOG Portable 48" H Play Pen - eBay (item 350375945012 end time Aug-23-10 07:58:03 PDT)
The one I have he jumps until he can get his front paws over the top then he pulls himself over the top. Do you think he could do that with one 4' tall? He weighs a little over 6 pounds.
I'd like to try maybe half days with him at the office and see if I can stop the barking behavior. If not, then at least he'd have something suitable to left in for long periods of time.