I can sympathize with your situation because I have the same problems with a couple of trees in my yard. Many trees, especially those that bear fruit, have a tendency to have low-hanging branches during the summer months. This is usually a result of additional weight caused by fruiting and is common on walnut, apple and crabapple trees, to name a few. Other trees such as pin oak, river birch and willow have a natural weeping habit, which contribute to the mowing problem.
Although many trees can tolerate minor pruning during the summer months to alleviate the mowing problem, oaks should not be pruned at this time. Oaks that are pruned during the summer months have a higher risk of infection by the oak wilt fungus. Members of the red oak group (red, black and pin) oak are rapidly killed by this disease, while members of the white oak group (bur, white and swamp white) oak die back more slowly.
I recommend pruning your oaks during the dormant season. If wounding your oaks during the summer months is necessary, wounds should be protected by a wound treatment compound (shellac) or paint (white latex). Under no circumstances should asphalt based creosote paint be used to treat wounds.
Another solution which would provide a better growing environment for your pin oak tree would be to apply mulch out to the edge of the branches. Mulching is a cost-effective method to reduce landscape maintenance costs and keep plants healthy. Mulching helps to conserve moisture because as much as 10-25% of the soil moisture can be lost through evaporation. Mulches help with soil aeration by reducing the soil compaction that occurs when raindrops hit the soil. They also reduce water runoff and soil erosion. Mulches help maintain a more uniform soil temperature (warmer in the winter and cooler in the summer) and promote the growth of soil microorganisms and earth worms when using organic mulches.