I want to plot several curves in pgfplots and I have problem with markers

I want to skip some of markers, but not skip Coordinates. For example if we have 24 Coordinates I dont need 24 marker, I need 12 marker with 24 Coordinates.
How can I do it?

\documentclass{report}‎
‎\usepackage{pgfplots}‎
‎\begin{document}‎
‎\begin{tikzpicture}‎‎
‎\begin{semilogxaxis}
‎%ar0 is a file with 24 coordinates
‎\end{semilogxaxis}‎
‎\end{tikzpicture}‎
‎\end{document}

-
Probably best to provide ar0.dat in your question to give people something to play with –  cmhughes Mar 14 '12 at 21:04

The key mark repeat=<each nth> allows to draw marks only at each nth position.
\addplot+[mark repeat=2] .... ;