You can use the grid.ResizingColumns event.
private void gridControl1_ResizingColumns(object sender, GridResizingColumnsEventArgs e)
{
if(e.Reason == GridResizeCellsReason.MouseMove && e.Width < 30)
{
e.Cancel = true;
}
}
If you want to handle things differently depending upon the column, you would also have to check the e.Columns property to see what column(s) is being resized.