How do I keep my 18 month old from wandering away whilst camping?

[GetToFalkirk]

We're going camping in North West Wales next week and I need some tips to stop my toddler running off.
We're going to a campsite which is near water (not too deep by all accounts) and he's a fast wee thing when it comes to running away. Do you have any tips on how to stop him? We've got an almost 4 year old daughter too but she'll be fine.
Thanks

Watch him?
Tie him up.
Duck tape him to a tent pole.
Hobble him like a horse.

Thought of all that but the strange looks from the other campers might put me off
I know I can watch him but not every second and it's easy to be distracted when cooking etc.
I thought about using the windbreaks as a pen but that seems a bit extreme.

soup beat me! I was going to suggest tethering him to one of the tent pegs. Or something.

On a more sensible note though, will he sit and play with lego or similar if you take a large tupperware box full with you while you're doing cooking etc? Or can DD entertain him with bribery as an incentive Or, if you have room, take the travel cot and use it as a playpen as and when you need to lock him in

we took a playpen it folded up in the back of the car, we used it for 3 years, when we changed to a caravan we still took it and used it it go across the opening in the awning, fab would not have been with out it, it was a babydan one, the travel one, www.ebay.co.uk/itm/Play-pen-/160637810906?pt=UK_Baby_Nursery_Furniture_ET&hash=item2566c278dalike this

or a travel cot, full size one though

I realise you may have already left, but what we used to do is to use one of those booster chairs which you have on a dining table chair, with a clip-on tray, and strap, set it on the ground and put dd in it. She couldn't stand up to escape as she was attached to the chair. A carseat on the ground would do the same thing, too.