I can't find the breath (sometimes I can, but the majority of the time I can't)

• I can't notice the rising and falling of the stomach even when lying and putting my hand on it and also to notice the breath in general is very hard for me.

Now I understand I can say if I don't notice it "knowing" or "breath" etc - but then I wait and wait and nothing - and in the mean time lots of secondary objects come up. If I follow them though its not good- because you should have a primary object to build concentration, so I need an "anchor"

So when I say "knowing" and then what should I do? Just focus on my belly? And if i don't feel anything? Not even in other areas like the nose - what should I do - focus harder? Follow secondary objects only?

I have practiced for a long time now (did retreats etc) and I thought this problem would fix itself, but I still have this problem. When I meditate I do 1 hour walking, then 1 hour sitting (mahasi style).