The landfills I have seen with the gas vent pipes around DFW do not have so many that it would be a huge issue to work around to have a flying field.
The WAMS club in Weatherford has had a decent flying site on a landfill for a number of years. There is a landfill in Dallas near Lewisville that we occasionally slope soar from....but it is still active in places and the aroma is less than enticing....
A landfill sure beats no flying field, but I am glad we (Fort Worth Thunderbirds) have a great field on US Army Corps of Engineers park property. It was featured in MA a couple of months ago. We were able to obtain a good bit of Corp funding for moving our field from one part of the park to another for safety reasons, but we in the club also put in about 60K to make it happen.
Let me extend an invitation to any AMA member to stop by and fly with us. The field is semi public and you do not have to be a member of the club to fly there. (We lease the property from the Corp) The field is on the south end of Benbrook Lake, just west of Mustang Park. Come by and fly sometime.
Aerial photos attached.