Can he pick up a signal from your router?
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He can look at getting a cantenna that will boost his recieving range. It is legal as long as he has your permission

WiFi Antennas-Super Cantenna Wireless Booster Antenna

This is an easy item to build yourself as well. Google for the plans and specs.
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I have used these before and can extend your wifi set-up to over a 1000 ft.

Outdoor Wireless Router & Outdoor WiFi Networks - Meraki Wireless