How to Check RPM's on Pony Motor?

How is the most common way to check the RPMs on the pony motor.
I tried to use a serometer(sp). (A length of wire on a spool calibrated to different frequency for different lengths). Because of where the pony motor is located and the fact that I can't find a flat surface close to the pony that will transmit enough vibration to get a reliable reading on the serometer.
So is there a cheap and easy way to check the RPMs? I really don't want to have to buy a digital tach just to set the revs.

In the center of the crankshaft where the flywheel is on is a small center dimple there and go get a cheap regular tack with a rubber tip on it and that,s the way I,d go.Just put the rubber tip in the center dimple there and observe the RPMs then and is so easy. That,s the way we checked RPMs at the shop on about everything till they came out with this high tech stuff for checking with the gun type.

Those laser tachs have come down in price compared to what they were a few years ago. If you go that route, try to check the calibration against an engine with a tach to make sire it's reading correctly. The nice part of the laser tach is that you can get a reading from a fair distance, you can get far enough away that there's no chance of getting clothing or hide caught in a rotating part.