I say board him. I once worked at a kennel, where we offered doggie day care, with a few "open" kennels for occasional visitors like your situation.
They were kept in fairly large kennels, with a blanket (or bed, if the owner chose to leave one) and taken outside at least every 3 hours for 30 minutes outside. If they were social dogs, we had two large grassy areas. If they were not able to play nice, they went into individual outdoor runs.
It was a great setup, and I'm sure you can find something similar for a fair price.
Maybe you have a neighbor you can trust to take him for the day, or at least go let him out. Or an acquaintance... My day's boss used to have me dog-sit for him whenever he went out of town.
If you find that you absolutely can't go with any other option, you might try making him a dog run with a harness. The harness will protect him from strangulation, and setting up a run will help keep him from getting tangled.
I would still hesitate to do that though... He is a cute, young, specific breed of puppy. A lot of people don't hesitate to steal dogs right out of your yard. It has happened to people I know, and is heartbreaking.