The Kent and Medway NHS and Social Care Partnership Trust, which runs Priority House in Hermitage Lane, Maidstone, wants to put up 3m high courtyard fencing with anti-climb guards.
The existing barriers are 2.3m.
In its planning application to Maidstone council, the trust said: “Patients continue to abscond over the fence putting themselves at risk of injury.
“It is hoped that the proposal in conjunction with the anti-climb gutter guard will prevent people from choosing this route to escape from the care facility.”
The unit is a medium secure centre for those suffering from mental health conditions. This means patients are not locked up, but do have restrictions on their movement.
The trust told the Kent Messenger this week that there had been a few escape attempts but that only two patients had absconded in the past six months. Both had been safely returned.
A spokesman said the proposed changes were also connected to its work with an Improving Safety in Mental Health collaboration, where NHS trusts and other health organisations join together to keep mental health patients safe.
At the Trevor Gibbens Unit, a secure centre on the same site which treats mentally ill criminals, there was one reported attempted escape in March 2011 in which a patient tried unsuccessfully to scale a wall and was caught.