A bulldozer is not a soil compaction tool/device. The tracks on the dozer are designed to spread out the weight so the dozer can better float over the dirt. Soil compaction tools are sheepsfoot rollers as pull behind or vibratory, and loaded pans. That is why these devices are sold as compaction tools. IMO and knowledge sheepsfoot devices are best because they knit the soil layers together as the layers are compacted. Packing clay layers with a dozer creates sheet layers that allows water to work it way through the soil layers. This is more pronounced when the soil lift layers are thick. From your description I think your pond has leakage due to poor clay compaction techniques. A good pond builder should know how to soil is best compacted especially for pond construction. .