How to place a copyright note at the bottom of a page after the footnotes?

The following patches parts of LaTeX's output routine and is not thoroughly tested, use with caution.

The following defines the macro \copyrightnote, it places its argument below the footnotes. The formatting is copied from LaTeX's standard definition of \@footnotetext. You should call it either in your preamble or after \begin{document} (just make sure it is before the first page was shipped out if you use it). The patching of the output routine is only done if you really use \copyrightnote.

\documentclass[]{article}

\usepackage{lipsum}
\usepackage{xpatch}

\title{Some Title}
\author{Mr Someone\\University of Somewhere}

\makeatletter
\newinsert\copyrightnote@ins
\count\copyrightnote@ins=1000
\dimen\copyrightnote@ins=8in
\newcommand*\copyrightnote@hook
  {%
    % place 
    \unvbox\copyrightnote@ins
    \global\let\@makecol\copyrightnote@makecol
  }
\let\copyrightnote@AtBeginDocument\AtBeginDocument
\AtBeginDocument{\let\copyrightnote@AtBeginDocument\@firstofone}
\newcommand*\copyrightnote@firstuse
  {%
    \gdef\copyrightnote@firstuse
      {\global\skip\copyrightnote@ins=\bigskipamount\gdef\copyrightnote@firstuse{}}%
    % backup to later restore it
    \global\let\copyrightnote@makecol\@makecol
    % after the actual footnotes are placed we place something else
    \xpatchcmd\@makecol{\unvbox\footins}{\unvbox\footins\copyrightnote@hook}
      {}{\GenericError{}{patching @makecol failed}{}{}}
    \copyrightnote@AtBeginDocument
      {%
        % trick the output routine to think there are footnotes, even if there
        % are none
        \ifvoid\footins
          \insert\footins{}% 
        \else
          \global\skip\copyrightnote@ins=\bigskipamount
        \fi
      }%
  }
\newcommand\copyrightnote[1]
  {%
    \copyrightnote@firstuse
    \copyrightnote@AtBeginDocument
      {%
        \insert\copyrightnote@ins
          {%
            \reset@font\footnotesize
            \interlinepenalty\interfootnotelinepenalty
            \splittopskip\footnotesep
            \splitmaxdepth\dp\strutbox
            \floatingpenalty\@MM
            \hsize\columnwidth
            \@parboxrestore
            \color@begingroup
            \parindent1em
            \noindent
            \hskip1.8em
            \ignorespaces #1\@finalstrut\strutbox
            \color@endgroup
          }%
      }%
  }
\makeatother

\copyrightnote{Copyright notice}

\begin{document}
\maketitle

\lipsum[1]\footnote{Some footnote}
\lipsum[2-4]
\end{document}

With a footnote:

Without a footnote:

You can use the package textpos, and define your copyright notice macro to insert a text block wherever you like. I use a similar command to place the company logos in my memos etc. Our company layout style requires that the logo is at an exact position, but since I always use A4 paper, it is easy.

My macro fix the text position relative to the absolute start of the page (0,0), so the copyright will end up at the exact place, whatever is written on the page.

If you need it differently, you can positioning the note relative to a paragraph, and you can calculate the position using calc syntax.

\documentclass[11pt]{article}

\usepackage{lipsum}

\RequirePackage[absolute]{textpos}
\setlength{\TPHorizModule}{1mm}
\setlength{\TPVertModule}{1mm}

\DeclareRobustCommand*{\copyrightnote}[1]{%
  \begin{textblock}{100}(35,280)
      \textbf{#1}%
  \end{textblock}%
    }

\title{Copyright under footnotes}
\author{Mr Someone\\University of Somewhere}


\begin{document}
  \maketitle
\copyrightnote{This text is copyrighted Mr. Someone}
  \lipsum[1]\footnote{Some footnote}
  \lipsum[2-4]
\end{document}

Not exactly what you need but too long for a comment/suggestion.

\documentclass{article}

\usepackage{eso-pic,xcolor}
\usepackage{lipsum} % dummy text

\AddToShipoutPictureBG{%
  \put(\LenToUnit{.5\paperwidth},\LenToUnit{2em})%
    {\makebox[0pt][c]{%
      \small\bfseries\color{red}\copyright Here is my copyright note!
      }%
    }%
}

\begin{document}
\lipsum
\end{document}