The Arnold Law Practice opened its doors in the Standard Oil Building in San Francisco on July 1, 1998.  Since that time Mr. Arnold has represented a wide range of clients in every aspect of environmental law, from contracts though litigation. Shortly after entering private practice in San Francisco in 1987, he represented a ranching family who saw their livelihood destroyed by pollution from the infamous Kesterson wetlands. After suing the government in the U.S. Claims Court, several million dollars was recovered for the government's "taking" of their property. A few years later, he represented Heublein Corporation in the environmental aspects of its $100 million acquisition of Christian Brothers. And, soon thereafter, he was the lead trial attorney for owners of a mini-highrise in a 10 week construction delay claims trial in San Francisco Superior Court. A number of other matters followed, involving representing property owners, buyers and sellers, before environmental agencies and in state and federal court in toxics cleanups, water and air pollution matters. The California voters enacted Proposition 65 in 1986, and in the early 1990s claims started appearing for alleged failures to warn for consumer products and emissions from manufacturing plants.

Today, Mr. Arnold represents clients in such areas as challenging condemnation proceedings for a failure to comply with CEQA, handling claims for title transfers under the federal Color of Title Act, and recovering insurance monies after defending "citizen suits" under the Clean Water Act. The Arnold Law Practice engages attorneys with specialities in other areas when required for client needs. The Arnold Law Practice also devotes significant resources to projects to improve the law and the community. Mr. Arnold has served for many years as an unpaid director on the board of the East Bay Services for the Developmentally Disabled, a provider of training and housing for developmentally disabled adults and seniors.