The charity I work for, Fields in Trust (formerly the National Playing Fields Association) protects parks, playing fields, open spaces and sports grounds. It protects through a Deed which is written in charitable and contract law, which means it protects against developments.
We protect nearly 3,000 sites across the UK, including many sports grounds - we're currently engaging with the ECB to be included on their club support pages.
The site needs to be nominated for protection by the landowners, but if they are keen to secure it, it can be done in weeks. Total cost - £80 in Land Registry fees to register the new Deed of title
www.fieldsintrust.org - PM me if you want more info...