I run a landscape company with a couple of crews and cannot keep track of when my crews arrive and leave a job

sounds like you need a better foremen,it,s his responsibility to make sure the workers are on the job and to keep track of their time. by letting your workers keep their Owen time records your leaving yourself wide open to over time charges and sloppy work.talk with your foremen and see Howe he reacts to him doing the time keeping.if he bulks or starts complaining he has to much to do now.it,s time for a replacement.. don,t know Howe big the crews are. but my nephew who is a landscaper also. had similar problems. he ended up hiring a women who was very qualified and she run,s a tight ship,might want to consider that.i was a supervisor for 25 years. and if you haven't figured it out yet..good help is hard to find...good luck