Thank you for your question regarding 25-ohm grounding in difficult conditions, it is our pleasure to help.
When you have a pole mounted transformer, you are generally dealing with a very small area of available soil (earth) that you can use for grounding. The resistance-to-ground of an electrode is determined by the local soil conditions and the sphere-of-influence of the electrode. In other words, the worse the soil, the more electrode you need. There really is no magic bullet to get around this.
The only way to guarantee a 25-ohm or less resistance-to-ground for your pole mounted transformer is to get an engineered grounding design. Using computer modeling, a grounding electrode can be designed to meet your 25-ohm requirement in local soil conditions.
For example, it may be possible that if you have a concrete pole, it may be possible to utilize part of the pole itself as an electrode. This could be supplemented with an electrolytic electrode system to achieve the 25-ohm requirement. But you won’t know this unless you do a proper design. Electrolytic electrodes are expensive and wouldn’t want to randomly install one of these grounding systems without knowing in advance that it will work.
E&S Grounding Solutions is of course more than happy to help you figure out what type of electrodes you need to achieve 25-ohms at your site (if it is even reasonably possible). All we need from you is soil resistivity data from the site and we can take care of the rest, all via email. But if not us, please get someone with the proper tools and experience to help you achieve this important standard.
Feel free to call us at 310-318-7151 California time, and someone will be happy to discuss your project with you , free of charge.
The Engineering Team at E&S Grounding Solutions
Photo credit: http://www.flickr.com/photos/st_a_sh/1444842019/sizes/o/in/photostream/