Public beaches are an occasion of sin. Even "mature adults" must not go there, as there is no good reason to put yourself in such an occasion of sin. Objectively speaking, people are running around mostly naked, in what most sane people would consider their underwear, exposing themselves in a manner fit ONLY for their spouses to see. There is no good reasons to share that much of your body with perfect strangers, married people of the opposite sex, or anyone else you're not married to.
Regarding the "glances at other women", keep in mind that the first notice or glance is usually accidental and totally without sin: he was merely looking in front of him, looking for his car in the parking lot, etc. It's that second, willful glance that leads to sin and sometimes a series of sins.
We must all mortify our curiosity, and keep custody of the eyes. Especially men.
It sounds like your husband is "damaged goods" more or less, since he used porn in the past. Porn objectifies women. Men preferring random women ("objects") instead of their own wife is NOT natural. Man desiring sex (usually more often than women) IS natural. Preferring only the kind of bodies (activities, behaviors, etc.) pushed by the porn industry is NOT natural OR universal. Your husband needs to continue his healing process from what porn has done to him, which is going to require a certain amount of corporal mortification and fasting.