Yes, I agree, it is very easy to stop a deer. Either give one loud whistle, or make one loud low-pitched "uuuuhg" sound from your throat, and they will stop dead in their tracks. Don't fumble around with a deer call to stop them. You don't need it.
But, you will only have about 5 to 8 seconds to shoot, so be sure that your rifle is up, and secure, with the safety off, and the deer in the scope or sights before you make the sound. Remember, even though they will have stopped, they will be totally jumpy and alert, trying to locate the predator.
The closer they are, then the less loud your noise should be. If they are really close (under 50 yards), and you make it too loud, then they will be startled and jump away. What you want to do is to make it loud enough for them to hear it and be curious, but not to scare them, and then they will stop to look and investigate. They are very curious animals.
And, very importantly, if the deer should throw up its tail and run away at the sound, then don't panic and don't shoot. 9 times out of 10, the deer will stop and look back within 50 yards, to see if anything is chasing him. Just relax and be ready to shoot when he stops and looks back.
Regards,
Mannyrock