We discussed a possible solution to this by using a similar stance system as Monk does. Instead of Terrain being a straight attack, it added certain effects to a handful of other skills, such as defense/offense/enmity modes.
Another, I think, would to let Terrain be a proc kind of skill, in a similar fashion to Sheild Bash as a Pally. Perhaps a mace/warhammer as their main hand and bell in the off-hand, with the bell coming out for certain skills.
FFXI actually had a fascinating take on GEO, but I feel translating that version would be better slated as a new flavor of healer as that job looked to be more of an AOE buffer from my research.
