Notices Dorothy's dog eats regular bites of foulest fungi (10)

'foulest fungi' is the definition.
'toadstools' can be an answer for 'fungi' (toadstool is a kind of fungus). I'm not sure about the 'foulest' bit.

'notices dorothy's dog eats regular bites' is the wordplay.
'notices' becomes 'ads' (advertisements).
'dorothy's dog' becomes 'toto' (Dorothy's dog in The Wizard of Oz).
'eats regular' becomes 'ols' (I am not sure about this - if you are sure you should believe this answer much more).
'bites' means one lot of letters goes inside another.
'toto'+'ols'='totools'
'ads' placed inside 'totools' is 'TOADSTOOLS'.

'of' is the link.

Can you help me to learn more?