The Standing Rules of the U.S. Senate allow a senator to anonymously notify his/her party leadership of an intent to object, preventing a motion from reaching the floor. Even though that person's name now has to be revealed after two days, if two senators join forces, they can take turns maintaining the hold in secret. This is yet another reason our Senate is only semi-functional.
"The very word 'secrecy' is repugnant in a free and open society; and we are as a people inherently and historically opposed to secret societies, to secret oaths, and to secret proceedings." ― John F. Kennedy