Good morning Greg.

Another option is the algorithm KGW (Kimoto Gravity Well)
http://bitcoin.stackexchange.com/questions/21730/how-does-the-kimoto-gravity-well-regulate-difficulty

This regulates difficulty.
If the difficulty goes up and left there, this algorithm regulates the difficulty after some time and lowers it.
For example if the difficulty is 20 and prohashing leaves, the network will lower the diff e.g. after 10 minutes to 15, then in next 10 minutes to 10, then after 10 minutes to 5 etc.
I am not sure how it works, but I found some coins who work this way.

In the above link someone wrote:
The goal is to have a more adaptive way of adjusting the difficulty instead of just averaging the last 2016 blocks like bitcoin. This is needed because of multipools which might switch the coin they are mining, and a sudden change in hashrate can occur (both increasing or decreasing). Especially when a multipool switches away you get stuck too long with a too high difficulty.