Keep calling.  My experience has been that techo music has plenty of
beat and no phrasing.  So dancers don't know when to stop the current
figure and start the next one.  Some figures like circles, stars and
lines forward and back have a kind of natural timing so dances with
those figures work well.  Some other figures such as heys, chains and
swings are less well defined as far as timing goes, and dancers tend to
rush heys and chains and go long on swings.  So the dancers will all
take different amount of time for them.  This means that if you stop
calling the various parts of the lines will start to diverge in where
they are in the dance and soon there will be parts of the room dancing
the A1 part while others places in the room they are dancing the A2 or
even B1 part.  I think swings may be the biggest issue.  Everyone likes
to swing and many dancers will go long on each swing, but they'll all go
long by a different amount.

    Choose dances with figures that have really well-defined timing and
don't stop calling and you will be OK.  You may be able to reduce the
amount of calling, but you will probably need to say something from time
to time to re-synchronize the dancers.

Jonathan