Step Turn,
In order to be confident any legal agreement is in any way effective, you need a lawyer: at the very least, you can claim against their indemnity insurance!
What you need to do before seeing a lawyer, is work out what you'd like to get in that agreement. Looks like you have already covered much of that - ie: grass cutting (most airfields leave the grass around the tyres for fear of being accused of slashing tyre walls accidentally), Of course, you may, instead, recommend that small concrete/slabbed pads for each wheel are put in place so the grass can be safely cut.
That's what I mean: you have to look at what you want, you have to look at ways of doing it (by legal agreement or by other methods), and then your lawyer will advise on what is possible under Canadian law.
One "trick"is to keep the Agreement very simple, and then put "regulations"- such as refuelling in certain areas, engine run-ups etc - in a Flying Order Book. Part of the Agreement is to follow the Flying Order Book. An example of how this can be useful is: in the Agreement all aircraft must be insured, in the FOB you enter the amount of insurance. So you can change the amount of cover required very easily.