mynd â = 'to go with'
mynd â'r ci = 'to go with the dog' which is transposed to 'to take the dog'
if you wanted to say "I am taking a dog for a walk" would it be "dw i'n mynd â chi am dro" or would that always mean "I am taking you for a walk?"
Well spotted! It could mean either. You would have to rely on the context of the conversation, or wait until I put the collar and lead on either 'you' or on a passing dog.
In practice, this is not a problem.