“The reason that I do not typically use the command word “stay” during training is because it is redundant.  If I instruct you to sit, I should not have to tell you to stay sitting.  What value is a sit without the stay?  Sit implies stay.  Once I have given the sit command, the assumption is that the dog should remain in that position until told otherwise.  That’s the standard.  The sit command can be considered the warning that it’s unacceptable to get up.  However, if you want to offer the additional information, you may say “stay” once the dog is sitting.  Then, that becomes the warning.  Only say it once.  That is the message that tells the dog of your expectations.  A warning should be delivered one time.  If the dog does not heed the warning, then the consequence must be delivered.  Otherwise, you will create a dog that will simply wait for the second or third or fourth warning word before changing his behavior.”