Hi,
Try using Bomix to stop the leaking in your pond. I did some research and you can buy it in Canada.
http://www.bomix.ca/produits.php?id=71&cat=rep&lang=en&p=22
Here are some more products to look at
http://rockwateruw.com/index.cfm?fuseaction=home
http://www.permacrete.ca/index2.htm
http://www.kryton.com/concrete_waterproofing.html
http://www.wired-2-shop.com/joneakes/ProductDetail.asp?ProdID=503&nPrdImageID=&CatID=27
As far as the safety of your fish you will need to check see if the products contain Calcium Chloride because that will harm your fish. You may need to contact them for the details.
Here in Australia we have a product that sounds the same as a couple of the products listed above, it’s called Quickset Watercrete and it’s safe to use in fish ponds and drinking water.
http://www.highwayhardware.com.au/new_product/2002_04/quickset.htm
I have used it to re-attach some underwater river rocks in my swimming. I would never have believed it could work if I hadn’t done the job myself. Its looks like normal mortar mix that you mix with water. I made a firm mix like putty placed a blob on the under side of the rock then submerged the rock in the water to the underwater rock ledge (about a foot deep). A small amount of grey clouding went into the water but the quickset watercrete patching cement held together and set the rocks firm onto the underwater ledge.
Hopefully the products available to you, do the some job.
Regards from Noelene