Recall problems when food/eating is available

Our puppy/ Dog (1.5 yrs old) I call him a puppy as it excuses his behaviour! His recall off the lead is okish- he follows our older dog when she comes back, but usually it doesn't cause a problem UNLESS he's eating grass or there's something far more tasty i.e poo, to be had than to come back. We use treats on and off (choose when to give it to them so they dont expect them everytime) but this doesnt always work. We try walking him on an extended lead and being consistent but when he's let off and is in a cheeky mood he will play up on re-call. The other issue is food- he is fixated with eating and is very greedy, fuelled by my dad's terrible habits of giving them toast crusts and bits of digestive biscuits so when he's snacking they sit below him expecting it too! So annoying when there's not a consistency for them (We have nagged forever!) Need re-call help, to stop his 'deciding' to come back or not.

He also eats our other dog's poo. No-one elses, just her's and we've tried all sorts; distractions, keeping him on the lead- he remembers where it is and runs back- even over a long distance! In the garden at night he'll feast on it!! Gross.

All help will be so gratefully received

George is the culprit in the photo ----->