It's secret deal and they don't have to put their names on it. They have been using it to block nominations. Democrats really hate to be beaten at their own games.

Simply explained on Wiki

"A secret hold is a parliamentary procedure within the Standing Rules of the United States Senate that allows one or more Senators to prevent a motion[to nominate] from reaching a vote on the Senate floor[is a form of Filibuster]. If the Senator provides notice privately to his or her party leadership of their intent (and the party leadership agrees) then the hold is known as a secret or anonymous hold. If the Senator actually objects on the Senate floor then the hold is more generally known as a Senatorial hold."

Standing Rules of the Senate
http://rules.senate.gov/public/index.cf ... SenateHome

Video: McCaskill
http://www.youtube.com/watch?v=FmBz2Q6klhs
Here, McCaskill offered the motions to nominate but an objection made.

This is the rule, McCaskill wants to abolish.

S.1 (2007)

An Act
To provide greater transparency in the legislative process.

TITLE V—SENATE LEGISLATIVE TRANSPARENCY AND ACCOUNTABILITY
Subtitle A—Procedural Reform
Sec. 512. Notice of objecting to proceeding.

http://frwebgate.access.gpo.gov/cgi-bin ... nr.txt.pdf

On page 25 of the above PDF

SEC. 512. NOTICE OF OBJECTING TO PROCEEDING.
(a) IN GENERAL.—The Majority and Minority Leaders of the
Senate or their designees shall recognize a notice of intent of
a Senator who is a member of their caucus to object to proceeding
to a measure or matter only if the Senator—

(1) following the objection to a unanimous consent to proceeding
to, and, or passage of, a measure or matter on their
behalf, submits the notice of intent in writing to the appropriate
leader or their designee; and

(2) not later than 6 session days after the submission
under paragraph (1), submits for inclusion in the Congressional
Record and in the applicable calendar section described in
subsection (b) the following notice:
‘‘I, Senator llll, intend to object to proceedings to llll,
dated llll for the following reasonsllll.’’.

(b) CALENDAR.—

(1) IN GENERAL.—The Secretary of the Senate shall establish
for both the Senate Calendar of Business and the Senate
Executive Calendar a separate section entitled ‘‘Notice of Intent
to Object to Proceeding’’.

(2) CONTENT.—The section required by paragraph (1) shall
include—

(A) the name of each Senator filing a notice under
subsection (a)(2);

(B) the measure or matter covered by the calendar
that the Senator objects to; and

(C) the date the objection was filed.

(3) NOTICE.—A Senator who has notified their respective
leader and who has withdrawn their objection within the 6
session day period is not required to submit a notification
under subsection (a)(2).

(c) REMOVAL.—A Senator may have an item with respect to
the Senator removed from a calendar to which it was added under
subsection (b) by submitting for inclusion in the Congressional
Record the following notice:

‘‘I, Senator llll, do not object to proceed to llll, dated
llll.’’.