Activist investors have been effective in blocking some big mega deals from getting done, and have made money in the process, according to The Deal's Senior Editor Ronald Orol. Orol looked at activist involvement in proposed deals that include Halliburton (HAL - Get Report) and Baker Hughes (BHI) , Staples (SPLS) and Office Depot (ODP - Get Report) , and Canadian Pacific (CP - Get Report) and Norfolk Southern (NSC - Get Report) .