I was wondering what fasteners if any others have used to connect the perimeter boards end to end?

I assume you're talking about corner brackets? I've used them all...from mending plates bent at a 90-degree angles to store-bought corner brackets in the shelving dept...but my FAVORITE all-time corner bracket is the one Iron Sleek put out starting last year. It's awesome.

http://www.ironsleek.com/backyard-rink- ... er-bracket

Yes, I sell them...full disclosure...but I sell them because I believe in them (but hey, buy direct from them, all good). I bought a case this year and actually use them around the house too (securing bookcases to walls, etc).

I like to use a minimum 2 foot length of the same dimension lumber to splice the boards together. Just butt the 2 boards end to end and then center the 2 footer on your seam. Deck screws work great to hold it all together - 6 screws per side for 2x10s and 8 screws per side for 2x12s.

Well I lay the boards down flat on the ground- end to end and straight as poss to the eye. decide which edge will be the top edge and align a 2 ft to 3 ft scab of 2x6 with the top edge fasten one board completely then move the 2 butts tight -align top edges again- and fasten. I do that for all 4 sides then turn them on edge and fasten the corners.
For the corners I don't do anything special and have had a corner blowout once but didn't loose water. I pack snow heavily on my deep side. ( 16 " to 18 " of water). I used to do concrete foundations years ago and we used a perforated metal strapping that came in a 50 ft roll. just nails a few 8d duplex nails on one side, bend it around the corner and put 1 nail at an angle to pull it taught and add a few more straight in after. it adapts to any condition cheap but not really reuseable because it will rust out after the first season.