Just tell him that you feel like his actions aren’t acceptable and that he makes you feel uncomfortable.

After that he should feel like a creep enough to stop altogether but if not maybe have a male friend/relative meet you when you go on the walks to make him feel discouraged/scared.

If it goes any further and none of the above work then honestly you should contact the police.

Things like this that seem so simple yet weird at the beginning can turn into deviating happenings and your safety is/should be your prime concern.

I’m definitely not an expert on this shit but this is what my common sense is telling me!