By blatantly watching, do you mean he watches other women and totally ignores you? Is he watching other women and constantly commenting to you about them ("she's hot", "she's got nice legs", etc.). Or is he just looking (passing glance) but not ogling (prolonged staring) but not making any comments while walking with you?
If he is ignoring you or making constant comments about every woman who passes by, then, IMO that's disrespectful to you. If it's merely a passing glance with no comment but his main focus is you, then I see no problem with that. When people are out walking, most of us do take notice of who passes us by. It's called being aware of your surroundings. If that's what he's doing, then no problem.