If you're not seeing the fog, you are either getting lucky and right on the edge, or you're not looking hard enough. Most anything after the 1 hour mark seems to produce fog according to my research.
As Argus said, pushing with Rodinal is not really ideal. It can be done as long as you are looking for that look. I actually wanted sharp, rough looking grain on some 6x7 negs I took a couple weeks ago - I souped it in Rodinal 1+25 for 8 minutes (shot at 800) with standard agitation. Well, with negs that big, I think I should have gone to a faster film if I wanted real grain, but they are deadly sharp.
You should do a search on stand developing here on APUG - there is a tonne of info. I think once you look into the reasons why stand developing works and how it does what it does, you will see that its not really very handy for altering the level of development with any degree of precision. Again, its a tool for a job, not a magic bullet.
Peter.