If you followed this advice with Aldabras you'd never get them to breed.
The safest thing is to put up a fence but another alternative is to provide a means of escape if the tortoise should fall in. As with anything in keeping tortoises there are a good deal of depends and there is no cut and dry answer.
In the case of the forest dwelling tortoises I don't think the dept of the water is a problem as long as you have sloping sides or stepped sides.
In the case of deset dwelling tortoises it might be a problem.
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Ed
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