user13355: Very broad question here.  I don't know exactly what the problem is but I'll edit this post as we narrow down the possibilities.
I think I'm running into memory constraints.
I'm running a sketch that records two temperature values every 60 seconds and transmits them to an AWS RDB via wifi.  It works well for about two hours then stops.  I don't know if it's a memory constraint but I suspect that it is.  What other common problems (often overlooked by newbies) can cause a sketch to end after a couple hours of run-time?
Is there a simple way to add an instruction to a loop to clear the SRAM?
Arduino UNO + WiFi 101
Edit #1 12/24/2015:It's the WiFi board.  It happily remains connected to my phone's hotspot but only lasts an hour or two on my home network.  Working on root cause...any ideas are welcome!
Edit #2 12/25/2015:Tried to Wifi.disconnect() and reconnect with no luck.  Why do some networks kick the board off while others work just fine?  Will look into the watchdog.

user13355: The problem was solved with a "soft restart" loop. Posts #10 and #11 are all I needed:
http://forum.arduino.cc/index.php?topic=49581.0

13355: <p>Very broad question here.  I don't know exactly what the problem is but I'll edit this post as we narrow down the possibilities.</p>

<p>I think I'm running into memory constraints.</p>

<p>I'm running a sketch that records two temperature values every 60 seconds and transmits them to an AWS RDB via wifi.  It works well for about two hours then stops.  I don't know if it's a memory constraint but I suspect that it is.  What other common problems (often overlooked by newbies) can cause a sketch to end after a couple hours of run-time?</p>

<p>Is there a simple way to add an instruction to a loop to clear the SRAM?</p>

<p>Arduino UNO + WiFi 101</p>

<p>Edit #1 12/24/2015:<br>It's the WiFi board.  It happily remains connected to my phone's hotspot but only lasts an hour or two on my home network.  Working on root cause...any ideas are welcome!</p>

<p>Edit #2 12/25/2015:<br>Tried to Wifi.disconnect() and reconnect with no luck.  Why do some networks kick the board off while others work just fine?  Will look into the watchdog.</p>
 13355: <p>The problem was solved with a "soft restart" loop. Posts #10 and #11 are all I needed:
<a href="http://forum.arduino.cc/index.php?topic=49581.0" rel="nofollow">http://forum.arduino.cc/index.php?topic=49581.0</a></p>
