Lock Horns and Hobnob
Make use of past opponents for long-term business development and network development.
The world of specialty law is a small one. Throughout your career, you will encounter the same attorneys you have once argued against. By using the proper techniques, you can maintain good relationships with other lawyers in your field, whether they are your allies or your opponents. Take advantage of prime opportunities to get on friendly terms with an attorney you observed to be a good advocate for his or her client.
Also, note which executives participated in the case; they can also be very good sources of future legal business and networking opportunities.
Don't Lose Touch
After an acceptable time has passed and your opponent has had a chance to lick his or her wounds (or vise versa), reach out to them. Congratulate the fellow attorney for a stellar representation of his or her client, them invite them out for coffee or lunch.
Keep in touch by email. Send the acquaintance copies of articles that you think they might be interested in. Inquire about upcoming conferences or seminars you might both attend.
Keep in mind that future new business opportunities may come from referrals, even referrals from former opponents.
As I mentioned, business executives are also good contacts for networking. Try a more subtle approach to continual law firm marketing. If you service a company on a project basis, such as a merger, invite the inside counsel and executives in direct contact with you out for social events or to a conferences to deepen (and perhaps solidify) the business relationship.