If you want to encourage wildlife into the garden, then you should ensure that the pond has different levels. We had a pond up until last year, we filled ours in to make more room as it was quite large.
If you want to encourage frogs and toads ensure that the top level of the pond allows for easy access in and out of the water.
We did a pond for my Dad a few years ago, its got quite well established now, he literally had thousands of baby frogs and toads


On the safety aspect, you can get some good barriers that sit on top of ponds, they are very strong, you can walk on them and they dont move but it depends what you want.
I agree with Jacob, safety has to be a top priority.