Reading this question : Simulating hand-drawn lines and following Percusse's idea I tried this :

But is it possible to "hide" the multido code in a style command and pass the parameters throu keys. By the way, for a step of 0.01, there is 101 marks but for a step of 0.2 there is only 50, and the line doesn't go to the end ?
\documentclass[tikz]{standalone}
\usepackage{}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin{tikzpicture}[decoration={markings,
mark=between positions 0 and 1 step .01 with {
\node at (0,.3pt*rand) [coordinate,
name=mark-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}]
{};}}]
\draw [help lines] grid (3,2);
\draw [postaction={decorate},help lines] (0,0) -- (3,1) arc (0:180:1.5 and 1);
\draw[smooth] [red] (mark-1)
\foreach \i in {2,...,101} {-- (mark-\i) } ;
\end{tikzpicture}
\begin{tikzpicture}[decoration={markings,
mark=between positions 0 and 1 step .01 with {
\node at (0,.4pt*rand) [coordinate,
name=mark-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}]
{};}}]
\draw [help lines] grid (3,2);
\path [postaction={decorate}] (0,0) -- (3,1) arc (0:180:1.5 and 1) -- cycle ;
\draw[smooth,red,fill=red!15] (mark-1)
\foreach \i in {2,...,101} {-- (mark-\i) } ;
\end{tikzpicture}
\end{document}
cycleand fill it with this methode. – Tarass May 19 '14 at 05:43\usetikzlibrary{decorations.pathmorphing}withrandom stepsdoes it as well. I've missed it. – Tarass May 19 '14 at 07:18