Nothing beats testing what amount of zap the fence is giving. You can buy a meter (don't get just a beeper, that just tells you it's live, not how big a belt it will give), or you can do it the old way, using a blade of grass.
Grass is a poor conductor, but it does conduct, so get a nice long, thick blade and hold it at one end. Drape the other end across the tape. If you get a sting, all is good, otherwise move your end closer and closer to the wire or tape until you do. If you had to get within an inch or so, that's not enough and won't bother anything. 3" is good.
Also, many people do not realise that (a) tape is very hard to join and not lose charge completely or somewhat; (b) if the tape is wound up twisted rather than flat, it will not work as well when you roll it out next time; (c) tape left out in all weathers will eventually deteriorate and the amount of zap it will give will reduce.
(Ask me how I know all this stuff....
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