i reacon these are simply snail eggs!!!! they like to lay them on hot things, and often found on the underside of leaves on pond plants too.

Without good photos and knowing where in the world you live one can only guess. (Any sort of wildlife question needs photo's or very detailed description and geographic information!) But, if you say it looks like a clear slug, a clear slug is a likely enough possibility. Why not look at some site with a lot of photo's of slugs?

One clear slug common in some areas is the Hedgehog Slug, which is an invasive species from Europe. Native slugs are good for the soil and play their role in the balance of nature. However, invasive species are almost always pests.
http://www.uky.edu/Ag/CritterFiles/casefile/slugs/arionintermedius.jpg

If you don't like your slugs one way to discourage them is to water your garden in the morning as opposed to in the evening. The idea is that the garden will have dried out before the slugs wake up and become active.

Slugs like beer. So do I. But no one, fortunately, puts out big swimming pools full of beer where I might fall in and drown. People do put out jars of beer to attract and kill slugs. I don't know if that counts as humane or not. There are certainly worse ways to die than drowning in beer.

Without a photo I can't be sure but it does sound like slugs. There are several commercial metaldehyde baits available but I have found that simple beer, yes beer, in a shallow pan is much more effective way to kill them, and even if non-target animals or bugs come in contact with it, like a bird bathing in it, it's harmless.

It's important to also eliminate the harborage by cleaning up leaf litter and reducing unwanted vegetation around your pond. It sounds like you're already doing that.