I could guard you could guard he could guard we could guard you could guard they could guard
V-ing form
I could be guarding you could be guarding he could be guarding we could be guarding you could be guarding they could be guarding
Perfect
I could have guarded you could have guarded he could have guarded we could have guarded you could have guarded they could have guarded
V-ing perfect
I could have been guarding you could have been guarding he could have been guarding we could have been guarding you could have been guarding they could have been guarding
Negation
Simple form
I could not guard you could not guard he could not guard we could not guard you could not guard they could not guard
V-ing form
I could not be guarding you could not be guarding he could not be guarding we could not be guarding you could not be guarding they could not be guarding
Perfect
I could not have guarded you could not have guarded he could not have guarded we could not have guarded you could not have guarded they could not have guarded
V-ing perfect
I could not have been guarding you could not have been guarding he could not have been guarding we could not have been guarding you could not have been guarding they could not have been guarding
Interrogative form
Simple form
could I guard? could you guard? could he guard? could we guard? could you guard? could they guard?
V-ing form
could I be guarding? could you be guarding? could he be guarding? could we be guarding? could you be guarding? could they be guarding?
Perfect
could I have guarded? could you have guarded? could he have guarded? could we have guarded? could you have guarded? could they have guarded?
V-ing perfect
could I have been guarding? could you have been guarding? could he have been guarding? could we have been guarding? could you have been guarding? could they have been guarding?
Interro-negative form
Simple form
could I not guard? could you not guard? could he not guard? could we not guard? could you not guard? could they not guard?
V-ing form
could I not be guarding? could you not be guarding? could he not be guarding? could we not be guarding? could you not be guarding? could they not be guarding?
Perfect
could I not have guarded? could you not have guarded? could he not have guarded? could we not have guarded? could you not have guarded? could they not have guarded?
V-ing perfect
could I not have been guarding? could you not have been guarding? could he not have been guarding? could we not have been guarding? could you not have been guarding? could they not have been guarding?