I think there are a number of unit funds available offering geared property investment for pension funds.
The key issue with gearing is that it increases the upside potential, while at the same time increasing the risk attaching to the investment.
I'm not aware of any rules applying at present (ie. limiting the extent of the gearing permitted in one of these funds), but it seems likely that the Revenue may have a view on this and may impose a limit if they feel that the level of gearing is becoming unacceptably high.
For an individual investor, you would need to consider your personal circumstances, including any other investments you have, your attitude to risk and how far away you are from your planned retirement age.
If in doubt, seek professional advice.
Regards
Homer