Nate, some of this stuff requires plenty of pain to learn better and better methods for doing things (experience). For instance, I very rarely ever reference an edge within my part model, and certainly not in the context of an assembly. The reason is that they'll go dangling so easily, as you've found out.
Instead, if I've got a round boss and I need to relate to it elsewhere, I create a relation to the sketched circle that created the boss. This way I cannot lose the relation unless I lose the boss itself (and its sketch), in which case I don't need to reference the boss anymore.
As to finding something like "Arc2", I've never figured that out. After spending about an hour on that task many releases ago I stopped trying. But my need to do so coincidentally disappeared as I began developing more and more robust methods for model-building. So the problem solved itself amidst the pain of gaining experience.
This can be very frustrating, but you really do make progress as you move along--particularly if you've got several hours each day dedicated to learning.
Let me know if I can be of any other help along the way:
Ah, Thank you Jeff.
The nugget here is to reference if at all possible, a Sketch, and not any convenient solid edge. Easier said than done, but certainly sage advice. I am very familiar with building robust models - in a different <eh-hem> "lesser" CAD package. In that software, I can reference edges, but Very Rarely Do, because I can constrain a sketch to a Plane - either solid or a ref. plane - the plane geometry is less likely to go away.
I am having some pain. And I am taking the time to learn, rather than just get the job done - this pays dividends in the long run.
My learning curve has been nice and steep these last couple of weeks - I am up to my eyeballs in two models for two clients - both of which are 100-200+ feature injection molded parts with multiple authors. One of them is nicely constructed - the other is a figurative rat's nest. I look forward to the day when I can start a project from scratch.
Thanks to a decent Help section, the ability to work at a client's occasionally where there are experienced users, and most of all this forum, I am able to be productive in this new world of SolidWorks.