<datagrid.cellstyle>
<style targettype="DataGridCell">
<style.triggers>
<trigger property="IsSelected" value="True">
<setter property="BorderThickness" value="0" />
</trigger>
</style.triggers>
</style>
</datagrid.cellstyle>
after i saw the examples i realized that i can create a setter on the property isselected and this solved my GUI problem