Hi
have used fiberglass tarps for many years with no problems Main problem is they come in bright blue ,silver and a dull brown lol.
An underliner is only necessary when you have roots,rocks that might puncture it. A good alternative is old carpet, you can often get that for free??
You can get the tarps in auto depts. of all the box stores in many sizes..
I'm not sure how the tarps would hold up to snow and ice as I live in s. florida but they have proven to be very UV resistant, particularly with the edges covered .
Good luck and let us know how it goes?? gary

Hey there, Aggierose. I haven't used all the different types of liners available. I have had to research and ask questions just as you are doing. While I respect Gary's opinion and recommendations, I would hesitate to use the fiberglass tarps myself because of all the critters that seem to use my pond. The raccoons and the muskrat would have torn up the tarp very quickly. You might have tree roots and rocks that could eventually cause problems. I went with the 45mil EPDM made by Firestone 11 years ago and have been quite happy with it for my 1000 gallon pond. It seem to be the most popular and cost effective way to go but others have different opinions based on their experiences.

On my first liner pond I got a 45mil EPDM liner on sale at a pet store at the end of the season for half price. Since then I have used roofing rubber (45mil Firestone EPDM) from Menards. Just about any home improvement store that sells roofing material sells the same thing. It is frequently on sale at a reasonable price.

If there is a lot of construction near you, you might be able to get a bargain price for a left over piece. There has been some discussion as to toxicity from the roofing material on this forum but I have not come across any post that claims it was harmful in any way. I have seen references to roofing material that was treated for resistance to moss and molds but I haven't actually seen any EPDM that included that for sale.

There have been numerous threads on this topic on this forum so you might want to do a search.

As for the underlayment, it depends on the soil composition. I have almost pure clay with no rocks and the tree roots grow around the pond rather than at it. Since the drainage is really bad, the materials I tried out rotted very quickly and I wound up using none at all. The smell was awful.

aggierose - I agree with the previous post. EPDM is a very wise choice as it easy to lay and comes with a 25 year guarantee. For underlay - a geotextile liner will give added protection and won't rot. I think best to add an underlay just incase a root does decide to grow towards your pond - they aren't that expensive and could save you from expensive and inconvenient pond liner repairs later on. Also make sure you are buying a liner for ponds (and not waterproofing for roofs) - pond liners are non toxic to fish - something I researched when decided to buy a rubber pond liner - 0.75mm EPDM.

Here is a link that might be useful: Liners Online

I wouldnt use a tarp especially if fish were involved. Tarps Ive gotten often have some sort of chemical repellent and sometimes have an oily feel and a solvent smell - get something known to be fish safe. 12 x 12 shouldnt cost all that much.

Hi
Often hear about the "toxic " properties of fiberglass tarps Certainly NOT my experience Have used them since 1981 both above and below ground . Raised 25 differnt species of tropical fish in them as well as over 40 species of plants. While I've had many disasters over the years "Toxic" was not among them. Oldest above ground was setup in 1985 Was relined due to the wipeout of the deep freeze of 09 and not one root had penetrated it . You guessed it I relined with a tarp lol gary

Hi
Here is a pic of the 5x10 using a tarp as a liner. . You have to look to the left at the waterline ,the silver colored part.. In the middle of summer can't see it at all.
This has been running continuously since 82 with a short break in 09 for the little ice age lol