For these calls its typically better to use a + b syntax since its gotten much faster in golang.

http://play.golang.org/p/7j6vPMB-zu
BenchmarkFmt	 5000000	       419 ns/op
BenchmarkPlus	50000000	        67.2 ns/op

So in this case you can use:
trailingUri := collection + "/" + key + "/events/" + kind