Thank you for your comments about my question - I appreciate them all. Luckily I was given some advice that changed my ideas about this. I applied sealant as I think you have described above - there is no longer any fold in the EPDM.
I have a short video which I took a while ago - before I was fully finished (I recently refined the top level). Take a look at http://www.bizconnector.com/MVI_1172.MOV
- please note that this is not streaming video, so you will have to wait a minute or two before it starts.
I would love any critiques about this. However, I have just recently discovered that there is a loss of water - a good 5-6 inches loss of water in the pond after a day. I am devastated! I don't know where the loss is happening, and I may have to wait until the Spring before I can investigate properly. Any ideas or suggestions about what I should do about this will be appreciated. I do wonder if there is a possibility that it will seal itself after a time (??).
I must say that I thoroughly enjoyed this project - I did everything myself, including moving every rock (some were very heavy) back and forth a few times to get the design 'just right'. It felt very creative, and I would do it again - but for the fact that it has this leak. Arghhh!