Navigation system address: Molenslag 2, Monster (i.e. just across the street from the Molenslag Campsite). Parking is tolerated off-season on that street, but you shall be fined in busier times. You could choose to drive a bit further on, towards the beach, but parking there is really expensive in the spring/summer (free off-season).
To locate the Hondendijk, place yourself so the beach is behind you (and so the camp site is to your left) and walk on the Molenslag (back towards Monster, away from the sea) until you reach the junction with the Laan van Delfland. The Hondendijk is located to the left of that intersection. You can recognize it by its wooden gate and the ‘losloop gebied’ sign.
Martino’s Ice Cream is not on the dike itself, but it is well worth the detour: easily the nicest ice creams I have had in my adult years. To go there from the Hondendijk, go back to the Molenweg (even further away from the sea and towards Monsterseweg), and you shall see a bunch of restaurants and snack bars (just in front of the windmill).
The dike is completely offleash.
What is so special about it?
A huuuuuge, fenced-off field with three different levels and a slow-running, shallow river if your dog fancies a dip.
As it is more or less made for dogs, you do not feel quite so apologetic for having a dog when you are there, and you can let your dog be a little more free (e.g. dig holes, run like a maniac, bark, etc.).
If you get off the field and back into the on-leash area (about in the half-way through the dike, if you head towards the sea), you can follow a spirally path up an 11-meter high mount for a panoramic view of the gorgeous dunes (Uitkijkpost Bloedberg).
What to look out for
I have heard many reports of poison there, but none from a direct source so I don’t know whether to believe them. Nonetheless, I haven’t been totally easy walking there since then.
I often witness dog-dog altercations there, which is quite inevitable given the long and narrow shape of the field (not always easy to keep your dog out of sight) and the high concentration of dogs.
Also, the Hondendijk pretty much runs a straight line: it is essentially a long field with a couple of trees. So it gets pretty boring after a couple of visits. But the dogs love it.
The other side of the coin with Martino’s Ice Cream is that the pavement on the Monsterseweg literally covered with day-old ice cream. Most dogs will scavenge this, with predictable stomach upsets or worse (dairy product past its shelf life on a summer day = not good at all).