Just to add my own experience in.

I have a female dog, who I raise since she is 4 months old. She's comfortable with me touching her.

When the first heat came, I helped her to explore carefully. She was insecure and I respected that. I expressed my own interest to her, but didn't push it any further when she didn't like it. Eventually though (about 3 months later), she made moves on me, wanting me to masturbate her (showed by pulling my arm and moving her lower half above my hand). Even though she was scared at first, she started to like it. Still I let her own freedom and didn't push it anywhere uncomfortable. Almost every time she wanted me to help her get reliefed, I did. This behavior started to grow from once a week to once a day eventually. To me, once a day is no problem at all and it seems like it will stay at that, as even through her second heat she didn't demand any more than that.

I did this always and exclusively in my own room (living with family). She has never tried to initiate anything when I was in other rooms or with other people and she has never tried to initiate anything with anyone else than myself.

Especially today, which is the reason why I'm posting here, she impressed me with her politeness about it. I was currently sitting in my brothers room, talking with him. My dog entered the room and lowered her head, looking at me. This is usually the sign that she wants me to follow her, so I did. She led me straight to our own room and expressed her interest in getting reliefed (as explained above). We had our business and went to sleep afterwards, being happy.

I even encouraged my dog and what happened today is the best proof to me that it's perfectly healthy for both her and me. I believe, when done right, your dog will understand what is good and what not when it comes to masturbation (or sex). Routines always work with dogs. Place, time and circumstances can easily be understood if you keep the routine up. Like I've heard someone else saying before, that putting a special blanket on the floor everytime you like to have sex (or whatever else) is a sign your dog can and will understand if done continually. This blanket will become the "sex blanket" to the dog. Of course, either he will jump right at you or he will decline politely if not interested at the moment.

Also, since you asked for male dogs: I've had a male dog before. Even though I tried to encourage him to masturbation, he was just not interested in it (if no female in heat was around). I gave up to it and only enjoyed the few times in the year when a female was in heat, so I could give both him and me some relief for that.

With this I do not decline that something like "obsessive behavior" exists. It can very well become troubling, but in my opinion this is mostly up to the caretaker of the dog. Care well for your dog and they will most likely care for you too.

Sex can be a hit or miss in general. Like some people are zoophile, others are not. Same goes for dogs.