Position plants and add oxygenators ... (ROSPA), children below the age of five are most at risk of drowning in garden ponds. The only way to avoid potential disasters is to not have a pond.
The best thing I have found to help wildlife is always have fresh water. Have water butts wherever rain comes off roofs.
The key to a healthy pond is keeping the water clear and ensuring that plants do not take over ... periodically by lifting it out with a garden rake.