Sette Chain Tensioner
The Sette Tensioner is a single speed chain tensioner that will work for vertical or horizontal dropouts. The Sette Tension Guide will easily mount directly to your rear drop-out and derailleur hanger and allow for full adjustability to achieve the perfect chain line.
I have used this for about 3 years on my bacl-up bike that I converted to single speed. Works as advertised, no issues.