Implementing a PPC Double Nelson
A PPC Double Nelson is a bottom rung strategy that skews spending towards long-tail keywords.
When an account is in Bargain Hunting mode, or when there is no (or very little) buffer between the bid limits and market price, an ad group can be underwater overall, but still competitive on the margin (for specific long tail keywords).
A PPC Double Nelson is set at the ad group level. To implement, set the bid amounts lower than the average historical actual CPC for the ad group, and set the the Ad Positions worse than the average historical positions (but not higher than 9). Generally, when the ad account element is under stress economically, one sets the positions below the fold. Squeeze the ad group hard enough and you can reduce spending to zero. Increase the bids slightly (at ad group level) and spending trickles to those keywords which are bargains on a CPC basis. You can also ease the Positions at the top end lower or higher to throttle the CPC for the long tail phrases.
A PPC Double Nelson does not take into account disparate conversion or bounce rates, so unless this is taken into consideration, a PPC Double Nelson can result in an arbitrary allocation of spending across all keyword phrases. For this reason, keywords which perform better than average should be segregated in their own ad groups (and those performing worse than average should generally be paused). While a PPC Double Nelson alleviates daily budget maintenance on the keyword level, it does not obviate maintenance overall. The ad group level bids, positions, ads, and keywords still require regular analysis in order to maximize ROAS.