As good as Craig Anderson has been for much of the season, the Senators are relying on him to do significantly more than most other goaltenders in the league not just in terms of games played, but in terms of shots faced. In order to continue their success after the All-Star Break and (hopefully) into the playoffs, the Senators badly need to tighten up their game defensively and offer Anderson (and Alex Auld, assuming he plays again this season) a little more support.
Anderson, as you would expect, leads the league in both shots faced (1,411) and saves made (1,284). He also leads the league in goals against (127), largely by virtue of those two figures.
On the other side of the puck, Ottawa averages 30.8 shots for per game, which is eleventh-best in the league. Their shots for-shots against factor is -1.3, which is 17th-best in the league (nowhere near as bad as Minnesota, at -5.3, or even the Nashville Predators, -3.5) but still leaves ample room for improvement.
The Pittsburgh Penguins have the league's best S/G-SA/G factor, averaging 7.8 more shots for per game than shots against.