How to keep vertices from snapping to to wrong-side of mesh when retopologizing? I've got a mesh that I'm retopologizing as a practice-run to get used to the motions, having followed the method described in this video by FlippedNormals.  Using 2.8, and settings are as follows:

 

Everything is working as-expected, except that when I try to extrude down the length of the arm.





Everything looks fine until I rotate the viewport and see that...



The vertices on the far-side of the retopology are snapping to points closest to the front, relative to the viewport at the time of extrusion.

Is there a way to keep this from happening, and instead just have them snap to the expected-surface of the mesh?  I'm not adverse to the idea of getting 2.79 and nabbing retopoflow should that indeed be the only/ideal solution, but I would definitely prefer to try and keep everything consolidated to 2.8

Thank you very-much, in advance!
You did not check "project onto self" in the snapping tab. Try that out and see if it helped.