I think there are a lot things to consider when making a wildlife pond and generally, having researched for a long time about size, siting, planting, maintenance, etc I was, to be honest, fairly confused. There are lots of conflicting advice about depth!
I understand Onopordum's assertions, generally and if living in a goldilocks location, then a shallow and broad pond might suit much better, if that's what is desired. Equally, all the photos on this thread illustrate how beautiful all wildlife ponds are.
However, in terms of the environment, when our local weather says it's been a beautiful, dry day with temps around 15, we can be sat under a blanket of snow ❄️ which never gets a mention. Likewise, when the rest of the country does have snow but it goes in a few days, we can still be snowed in after 10 days! The army has been known to close the roads to the village before now 🙄 So, there are situations where a wildlife pond being deeper offers a stable environment for all those inhabitants who need to have consistency. The wind chill alone can take your skin off up here, believe me and there's no shelter apart from the lee of the drystone walls we put in the garden.
Micearguers, I hadn't thought of the stability of the pond in terms of nutrients, etc - very interesting. We had to build up the one end of our pond (seen in above photo) because of a slope down the garden and the camber across. Consequently, we have that area multi-shelved and will place a log and other easily accessed escapes, as it sounds like you are doing. The bog garden at that end is hopefilly going to be a nice compliment to the woodland bed at the other end and the planting all the way around it, too.
We have decided to position a couple of massive granite boulders, taken out of the soil, to act like silent guardians over the garden. We have so many! But the garden is too small for ma of the evergreen shrubs I love (viburnum Titus being one) because they get so big. So, the boulders will quickly be colonised by mosses and lychens and look beautiful standing alone in winter or when the planting engulfs them!
Now, the weather says snow ❄️ is on the way so I'd better get the Factor 50 out!