Certainly you can depend on us going wrong! (6)
I believe the answer is:
surely
'certainly' is the definition.
(synonyms)
'depend on us going wrong' is the wordplay.
'depend' becomes 'rely' (to depend on someone is to rely on them).
'on' means one lot of letters go next to another.
'going wrong' indicates an anagram.
'us' is an anagram of 'su'.
'rely' after 'su' is 'SURELY'.
'you can' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for surely that I've seen before include "Undoubtedly" , "that's for certain" , "it would seem ironic?" , "With certainty" , "Indubitably" .)