Avoid access to previous design work. Negotiate for improved warranty and compensation clauses. Send a cease and desist letter telling the offender to stop using their work. You can submit it yourself, but for the most impact, ask your lawyer to send it.
If someone else infringes your intellectual property rights, you must take steps to prevent them from doing so. You can start by contacting the person directly and trying to resolve the issue in a friendly way. If these efforts fail, you'll have to take the case to court. For example, you can ask the court to prohibit the offence in a provisional injunction proceeding (kort geding).).
Or you can request that infringing products be removed or destroyed. Other options are to request a share of the profits or to require access to information about buyers. If you start to market your invention or otherwise disclose it to the public before applying for patent protection, remember that you must file your patent application within one year of the disclosure and be the first to file it, or you will lose your right to protection. Many countries require that you apply for patent protection within one year of the disclosure of your invention.
An experienced intellectual property lawyer can help you evaluate what protections are right for you, as well as defend your rights. Another type of protection, sometimes used for printed reference materials, involves including fictitious entries or deliberate disinformation in the body of the work to track down competitors' copies. Thanks to the Berne Convention for the Protection of Literary and Artistic Works, works originating in any of the signatory countries receive the same protection in all other signatory countries as those countries grant to works originating in those countries.