Rune Fencer is the first job I've seen for which a Stoneskin II spell would make sense, given that it's a tank that relies heavily on Enhancing Magic. This theoretical Stoneskin II would still be self-only, but stronger, as befits a defensive spell exclusive to a job intended to tank.

How I'd design it:
* Enhancing Magic, obviously.
* Still self-target only. (Compatibility with Accession is an open question.)
* RUN95 (in other words, don't make us gain a bunch of job points just to get better general damage mitigation; this should be something all RUNs should be reasonably expected to have). No other job receives it.
* Costs 44 MP (151.7% of Stoneskin I's cost).
* Damage absorbed cap of 525 (150% of Stoneskin I). The formula should make this cap within reach of a RUN99 with item level 109 gear (in other words, let it be fully effective for a relatively new RUN so that people easily accept the spell's usefulness and relevance).
* Base duration of 6 minutes (120% of Stoneskin I's base duration).
* Base casting time of 8 seconds (80% of Stoneskin I's base casting time).
* 45-second base recast (150% of Stoneskin I's, occasionally making it necessary to use Stoneskin I as a stopgap measure).
* All existing Stoneskin-boosting gear would also be compatible with Stoneskin II.

I believe that if such a spell were added to Rune Fencer, made accessible in the mid-90s levelwise, and made easy to raise to its full base effectiveness, people might take RUN somewhat more seriously as a tank.