Your audience management efforts are really very little different for an outdoor venue from an indoor venue - both require advertizing, ticket sales, and house management. You may not have hard walls and doors, but your can establish a perimeter and manage access via designated entry gateways.
There will always be onlookers from outside the perimeter, but if the show is good enough and your ticket prices reasonable, then you should be able to 'sell' the idea to the outliers to join the audience and get a better vantage point. Don't be above playfully mocking them for the entertainment of the key patrons (this teaches the players how to deliver an 'aside', too.). It is possible to shame them into tossing a few bucks your way for a cheap seat. If you are 'passing the hat', then be sure to include the outliers, too.
A side note to consider is that you will need to rent / borrow / buy an assistive listening system (ALS) to serve your audience just as you would with an indoor venue. This is an ADA requirement. Infrared type systems don't work so well in bright daylight, so FM Broadcast (72 MHz or 216MHz) or Hearing Loop systems are usually more achievable. Hearing loop type system will require you to bury a perimeter cable a few inches in the ground (usually a #12 THHN conductor will suffice, so if you have a paved seating area it is typically best to use an FM type system).
Training your actors to project is vital to this type of venue, as there are typically not walls or ceilings to provide beneficial acoustic reflections. A sound system outdoors will still present the same gain-before-feedback challenges as does an indoor system.
Other issues you may have to contend with are rain (keeping the electronic gear dry can be a challenge), wind (secure scenery, trusses, and towers properly so NOTHING can blow-over), emergency venue evacuation plans (go to the Event Safety Alliance web site and purchase a copy of the Event Safety Guide - it applies to ALL types of indoor and outdoor events), safe power (GFCI protected power circuits may be required, making sure that EVERY device has a good electrical ground is vital to a safe electrical system. This is no time for zip cord), insect and rodent infestations, poison ivy / poison oak (if you are clearing underbrush), and heat (heat stroke is a very real threat to workers and performers).
My past experience with Shakespeare In The Park type shows has been a great memory, so make it happen!
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Erich Friend
Theatre Consultant
Teqniqal Systems
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