what can be causing my dog to have seizures?

[GingerDanMason]

We have a 4 year old Blue Heeler, we live in town.....Hank spent half his time outside in a pen (when we are gone) and half his time inside (when we are home).  He shared a pen with a Black Lab.....last Fall our black lab died tragically.  I don't like to think about it, because it was our fault, but we didn't realize it, until it was too late.  After that, Hank was always inside when we were home and then he started having seizures.....it was hard to determine if he had any when we were at work, because he stays outside in the pen when we are gone.  One day, we witnessed 4 seizures, so we took him back to the vet and he was put on phenabarb.....that stopped the seizures and all was good, until we noticed him coughing all the time and just not acting right.....we took him back to the vet when we noticed bloody stool.......he had to stay 2 nights at the vets office, so they could watch him closely and do some tests....his prostate was enlarged....his throat was very red, his lymph nodes were enlarged, his blood work came back abnormal, he had bloody stool......his GI Tract was inflamed.....the vet said the phenabarb had caused it, so we took him off the medicine.   For a few months, we never saw one seizure until this morning and he had 4 grandmal seizures right after another, lasting 20 minutes or longer........we kept the phenabarb and so we gave him one until we could take him to the vet....we were thinking maybe if we just kept him on them for a shorter time frame that everything may even out....it sure isn't gonna hurt at this point, so we put him out in the pen along with our other Heeler, so they could keep each other company, because he kept pooping in the house, not being able to control it.  When we got home, we brought them in and he had 2 more seizures right after another. This time  it only lasted 5 minutes......I had already cleaned up 2 messes and it was bedtime, so we decided to put him and our other dog out in the pen over night.  We are taking him to a different vet to get a second opinion......do you suggest anything else to do?