Parent starts wandering. What kind of precautions should I take?

my dad had a stroke about 15 years ago and is know 92 and in good physical health for his age. With the stroke came confusion and a general problem with understanding, being able to make sound judgement etc. His mobility (falling) is increasing, and his person higiene has decreased.
We've adapted to these changes.
Today for the first time, I got a call from my neighbor up the street at 7 AM saying my Dad was at their house and he was wearing only his underwear.
While I know that his confusion would continue to get worse, this was unexpected. What kind of precautions should I (and my mother) be taking?

Thanks