This is a serious situation. You did nothing wrong, and you are not alone. Report the incident to the Dutch police by calling 0900-8844 (non-emergency) or visiting a police station; this helps document the harassment and may prevent it from happening to others. You can also contact Slachtofferhulp Nederland (Victim Support Netherlands) for emotional and practical support, regardless of whether you file a report.
When you call the police, explain clearly what happened: the location (Stratum), the time, the man's description (age, clothing, any distinguishing features), and that he was touching himself in public. You can ask for an interpreter or bring a Dutch-speaking friend. The police take public indecent acts seriously, and your report adds to their awareness. If you feel unsafe in the area, consider changing your dog walking route or times for a while, and stick with your dog parent group.
Tradeoffs: Filing a report can be emotionally draining and may not lead to immediate prosecution, but it creates a record that can help if there are other reports. Slachtofferhulp offers free, confidential support without requiring a police report. You can also talk to a trusted neighbor or a local community center (buurtcentrum) for informal advice. Your feelings of anger, fear, or shame are valid; seeking support is a strength, not a weakness.
Concrete next steps: 1) Write down everything you remember now while it is fresh. 2) Call 0900-8844 or go to the nearest police station (Eindhoven centrum has one at Mathildelaan 4). 3) Contact Slachtofferhulp via 0900-0101 or their website. 4) Share with your dog parent group so they can watch out. 5) If you want to learn Dutch phrases for emergencies, focus on "Ik word lastiggevallen" (I am being harassed) and "Help, bel de politie" (Help, call the police). Your safety and wellbeing come first.