You might think about Y chromosome DNA testing. While it will not provide the certainty of a paper trail, it could very well show you where it would not be profitable to look. E.g., if your ancestor was a Thomas who adopted the Fraser name, that is likely to turn up. It show probabilities, and is a good way to get an informed idea of where to look further, and where further research would be futile. The largest and best DNA testing service is at www.familytreedna.com. Take a look at their FAQ, it's fairly exhaustive.