A very simple solution with pstricks: defining four nodes and connecting them with the relevant parameters:
\documentclass[svgnames]{amsart}\usepackage{array}\usepackage{pst-node}\usepackage{auto-pst-pdf} %% to compiile with pdflatex -shell-escape (TeX Live, MacTeX) %% or pdflatex --enable-write18 (MiKTeX)\begin{document}\[ \begin{postscript}\setlength{\extrarowheight}{3pt}\begin{array}{|c|c|c|c|}\hline& Dig & \Rnode{W}{Weed} & Cut\\\hlineBoris & 50 & 0 & 50\\\hlinePercival & 20 & 0 & 30 \\\hline\pnode[-4pt, 0.7ex]{A}Spike & 0 &\Rnode{O}{0} & 0\pnode[4pt, 0.7ex]{B} \\\hline\end{array}%% Node connections:\psset{linewidth=0.6pt, linecolor=Crimson, linestyle=dashed, dash=3pt 3pt}\ncline[nodesep=-9pt]{W}{O}\ncline{A}{B}\end{postscript} \]\end{document}
